Israel began a military offensive in the northern part of the enclave several weeks ago, targeting what it said was a regrouped Hamas presence in the area.

The Israeli military confirmed the strike in Beit Lahia in a statement on Sunday, saying the air force had “conducted a precise strike” targeting Hamas fighters, adding that it had taken steps to “mitigate the risk of harming civilians.”

The Palestinian Authority’s news agency Wafa, citing medical sources, said 40 people were killed in the strikes and 80 others were wounded, including women and children.

The situation in northern Gaza has become “unbearable,” Stéphane Dujarric, spokesman for the United Nations secretary general, said Sunday, adding that 60,000 people have been displaced in the past few weeks.

Israel’s renewed military operations have resulted in “widespread devastation and deprivation,” Mr. Dujarric said, which “are making the conditions of life untenable for the Palestinian population there.”

On Friday, Volker Türk, the U.N. high commissioner for human rights based in Geneva, said in a statement: “Unimaginably, the situation is getting worse by the day. The Israeli government’s policies and practices in northern Gaza risk emptying the area of all Palestinians. We are facing what could amount to atrocity crimes, including potentially extending to crimes against humanity.”

Farnaz Fassihi contributed reporting.

Israel invaded southern Lebanon this month to fight the militant group Hezbollah, which is Shiite Muslim and backed by Iran. Sidon is largely Sunni Muslim, and Israel has not ordered civilians to evacuate the city, as it has for a number of other towns or city neighborhoods across Lebanon.

There was no immediate comment about the strike from Israel’s military, which said earlier that it was carrying out “targeted ground raids” in southern Lebanon. The military also ordered civilians to evacuate 14 other villages in the area and move north of the Awali River, which runs around 35 miles north of the border with Israel.

More than 1.4 million people, or nearly a quarter of the country’s population, have fled their homes in Lebanon, according to an estimate by the United Nations. The Lebanese authorities have said that more than 2,600 people have been killed since last October, when Hezbollah started firing missiles and drones at Israel in support of the militant group Hamas in Gaza and Israeli forces responded with airstrikes and assassinations.

The Israeli military said Sunday on social media that it struck Hezbollah facilities for manufacturing and storing weapons in the Dahiya, a dense set of neighborhoods south of Beirut that is a Hezbollah stronghold. Israel also said its operations had killed around 70 Hezbollah members over the past day and that on Friday it had killed two local Hezbollah commanders who operated around the town of Bint Jbeil, which is close to the border.

There was no independent confirmation of the statement.

The invasion and Israeli airstrikes in Lebanon have eliminated much of Hezbollah’s top leadership, but they have not stopped the group from launching cross-border attacks.

Israel’s military said that a total of 90 projectiles were fired at Israel on Sunday in two separate waves. It said that some had been intercepted, while a drone strike hit in the Bar-Lev industrial area, about 13 miles south of the border. The statement gave no details of whether it caused any damage.

His remarks came as U.S. and Israeli officials were expected in Qatar on Sunday in an effort to revive talks for a cease-fire between Israel and Hamas. Beyond the Iran strikes, Israel’s recent killings of Hamas’s leader in Gaza and the leaders of Hezbollah in Lebanon loomed large over the meetings.

David Barnea, the head of Mossad, Israel’s foreign spy agency, was due to meet in Doha with William J. Burns, the C.I.A. director and lead American negotiator in efforts for a cease-fire in Gaza. Mohammed bin Abdulrahman Al Thani, Qatar’s prime minister and foreign minister, was also expected to participate.

In statements issued before the weekend, Mr. Netanyahu’s office stated that Sunday’s meeting was aimed at advancing several initiatives, including one being promoted by Egypt, which along with Qatar has acted as an intermediary between Israel and Hamas.

An Israeli official familiar with the discussions said the Egyptian proposal involved an initial deal that would see a few hostages released during a short pause in fighting in Gaza. The idea, the official said, would be to get the ball rolling after months of impasse. It would also test Hamas’s decision-making process after the killing earlier this month of the militant group’s leader, Yahya Sinwar.

Later Sunday, President Abdel Fattah el-Sisi of Egypt said the initiative would see four hostages released in exchange for a number of Palestinian prisoners in Israeli custody during a two-day pause in the fighting in Gaza. Speaking at a news conference in Cairo, Mr. el-Sisi presented the idea as a preliminary step leading to talks for a comprehensive cease-fire.

U.S. and Qatari officials have said it was unclear whether Hamas might be willing to re-engage in revived cease-fire negotiations.

Hamas officials have stated repeatedly, however, that any deal would be predicated on the Israeli military’s withdrawal from Gaza and an end to the war there — conditions that Mr. Netanyahu has not been willing to agree to so far. The Israeli authorities have said that at least a third of the 101 hostages still being held in Gaza are dead.

A senior Biden administration official, who briefed reporters soon after Israel’s strikes on Iran, said the United States was “prepared to lead an effort” to end Israel’s war against Hezbollah in Lebanon over the coming days — as well as an effort to finally achieve a cease-fire in Gaza and a return of hostages held in the enclave.

The official, who spoke on the condition of anonymity to discuss sensitive matters, said the overall contours of those arrangements were in place and that it was “time to bring these deals to a resolution once and for all,” according to an official transcript of the call.

The diplomatic maneuverings came as Israel held state memorial ceremonies on Sunday tied to the Hebrew calendar’s anniversary of the Oct. 7 Hamas-led attack on southern Israel that prompted the war.

President Isaac Herzog of Israel, whose role is mostly ceremonial, echoed widespread hopes that the country’s recent military gains might translate into political achievements that could bring more stability to the region.

“The elimination of the arch-terrorist Sinwar and other enemies, and the impressive fighting by the IDF and security forces, have created an opportunity that we must not miss,” Mr. Herzog said at the official memorial for the hundreds of Israeli soldiers killed over the past year, referring to the Israeli military.

Israel’s defense minister, Yoav Gallant, noted that “not every goal can be achieved through military action.”

“Force is not an end in itself,” he said at one of the ceremonies. “When it comes to returning the hostages, we will be required to make painful compromises.”

Nadav Eyal, a prominent Israeli political analyst, wrote on Sunday in Yediot Ahronot, a popular Hebrew daily, that the military “has delivered achievements” but these were not enough on their own.

A substantive victory would be “one in which Israel emerges from the war more secure because the reality beyond the battlefield has changed,” he wrote.

Gabby Sobelman and Myra Noveck contributed reporting.

President Masoud Pezeshkian of Iran warned late Saturday that his country would “answer any stupidity with wisdom and strategy.”

Ayatollah Ali Khamenei, Iran’s supreme leader, has the authority as commander in chief to order strikes on Israel. On Sunday, in his first public comments about the attacks, Ayatollah Khamenei said that the effect of the strikes “should neither be magnified nor downplayed,” the Iranian state news agency IRNA, reported. He did not appear to explicitly call for retaliation.

In the meantime, Iran’s foreign minister, Abbas Araghchi, has asked the U.N. Security Council to convene an “urgent meeting” and condemn the attacks, IRNA reported. It said that Mr. Araghchi sent a letter to the United Nations secretary general stating that Iran “reserves its inherent right to legal and legitimate response to these criminal attacks at the appropriate time.”

Farnaz Fassihi and Mike Ives contributed reporting.

The Iranian and Israeli officials familiar with the attacks spoke on condition of anonymity to discuss intelligence.

Israel’s destruction of the air-defense systems has raised deep alarm in Iran, the three Iranian officials said, as critical energy and economic hubs are now vulnerable to future attacks if the cycle of retaliation between Iran and Israel continues.

“Israel is sending a clear message to us,” said Hamid Hosseini, an expert on Iran’s oil and gas industry and a member of the Iran-Iraq Chamber of Commerce. “This can have very serious economic consequences for Iran, and now that we understand the stakes we need to act wise and not continue the tensions.”

Iran’s military announced that four soldiers working with air defenses were killed in Israel’s attacks. The Iranian media said the casualty numbers would probably increase.

Two of the soldiers were identified as natives of the city of Mahshahr, the closest residential town near the Bandar Imam Khomeini petrochemical complex.

Two Israeli officials said that initial plans, developed immediately after Iran fired waves of ballistic missiles at Israel in early October, included strikes on targets linked to Iran’s energy industry and nuclear project.

But while Israel was planning, the United States urged it not to strike any of Iran’s energy and oil sites or nuclear facilities, fearing that attacks on such valuable sites could draw a heightened Iranian response, destabilize the global economy and set off an all-out regional war that could draw in the United States. In its strikes on Saturday, Israel eventually decided to attack the air defenses around several energy facilities but did not target the facilities themselves, the Israeli officials said.

Iranian officials, including Foreign Minister Abbas Araghchi, had repeatedly told the news media, and regional Arab counterparts in diplomatic meetings, that Iran’s energy infrastructure was a red line, and that if attacked Iran would respond forcefully. Mr. Araghchi sent a letter to the United Nations on Saturday urging the condemnation of Israel and calling its attack “unlawful and aggressive” and “against the sovereignty and territorial integrity” of Iran.

The Iranian armed forces issued a statement on Saturday saying that Israel’s attacks had targeted radar air-defense systems in Khuzestan, Ilam and Tehran, causing minor damage. The statement said repairs were underway and that Iranian air defenses had succeeded in neutralizing most of the Israeli missile and drones.

The three Israeli officials said that command-and-control trailers, as well as the radar system, were among the targets struck on Saturday. According to Israel’s assessment, the systems were severely damaged and rendered inoperative. One of the officials said that satellite imagery post-strike would show that Israel hit only the air-defense battery of the Imam Khomeini petrochemical complex, avoiding the nearby industrial complex.

The Iranian military, in its statement, added that Israeli fighter jets had not entered Iran’s airspace and had fired missiles and drones from Iraq’s airspace. The military blamed the United States for allowing Iraqi airspace to be used, and Iran’s mission to the United Nations accused the United States of “complicity in this crime.”

American officials have said the United States played no role in Israel’s attacks against Iran.

Iran’s Supreme National Security Council held an emergency meeting on Saturday, and military commanders briefed its members on the scale of damage and the targets, according to the three Iranian officials. The council discussed how Iran should respond but no decision has been made, they said.

Ayatollah Ali Khamenei, Iran’s supreme leader, has the authority to order strikes on Israel as the commander in chief. He is expected to make public comments about the attacks on Sunday.

In addition to striking the defenses around energy sites, Iranian and Israeli officials said, Israel’s attacks have effectively taken out four S-300 air-defense systems that Iran had purchased from Russia. Israel disabled one in April in an attack on a military base in Isfahan Province and three on Saturday, at Tehran’s Imam Khomeini International Airport and the Malad missile base on the capital’s outskirts.

“This looks like a potential preamble to a much more effective strike against Iran’s infrastructure and even nuclear sites,” said Ali Vaez, the Iran director of International Crisis Group. “Iranians don’t have the capacity to replace these systems in a timely manner, which renders the country much more vulnerable in future tit for tats.”

In addition to the air-defense systems, three major missile manufacturing bases — Falagh, Shaid Ghadiri and Abdol Fath — belonging to the Revolutionary Guards Corps were also attacked, according to the Iranian and Israeli officials. The Parchin and Parand military sites were also attacked with drones, the officials said.

Israeli officials said the attacks had set back Iran’s ability to build missiles, but Iranian officials disputed this, saying the damage was minor and the setbacks short term.

The energy facilities whose defenses were struck are critical to Iran’s ailing economy, which has struggled with U.S. sanctions, inflation and other problems for years. Khuzestan Province, in southern Iran, is home to most of the country’s oil and gas fields. The Bandar Imam Petrochemical Complex is Iran’s largest such compound, generating millions of tons of petroleum-based products annually for export. The Abadan refinery is Iran’s largest oil refinery near the Persian Gulf, with a capacity of 360,000 barrels of crude oil per day.

Israel’s targeting of air-defense systems around the energy sites was similar to its attack in April, when it struck the radar system of an S-300 air-defense system near Natanz, a city in central Iran that is critical to the country’s nuclear program. The April strike came in response to Iran’s launching several hundred missiles and drones at Israel, a barrage that was itself a response to an Israeli airstrike on Iran’s embassy compound in Damascus.

With Iranian proxies like Hezbollah dramatically weakened, more hawkish Israelis had argued that they were being handed an opportunity to move forcefully against their regional archenemy, Iran. Some proposed attacking the Iranian nuclear program, long a source of existential dread for Israel.

After Iran launched a wave of ballistic missiles on Israel on Oct. 1, the Biden administration urged Israel to moderate its response and avoid targeting either oil or nuclear sites, which U.S. officials feared would set off a wider war — one that would ultimately draw in the United States.

Yair Lapid, the centrist leader of Israel’s parliamentary opposition, criticized Mr. Netanyahu’s government for ultimately deciding on targets that aligned with Washington’s requests. Mr. Netanyahu’s office later denied that Israel had not struck Iranian oil and nuclear facilities because of U.S. pressure.

“The decision not to target strategic and economic targets in Iran was a mistake,” Mr. Lapid said. “We could and should have made Iran pay a much higher price.”

Mr. Ben-Gvir had also criticized Israel’s response to a direct Iranian attack in April — a strike on an antiaircraft battery — as too feeble.

Saturday’s attacks should be followed by further action aimed at “damaging Iran’s strategic assets,” he said. “That must be the next stage.”

Avigdor Lieberman, a hawkish ally-turned-critic of Mr. Netanyahu who leads the right-wing Yisrael Beiteinu party, similarly slammed the Israeli government for not going far enough.

“Unfortunately, it seems that instead of exacting a real price, the Israeli government is satisfying itself with operations that are purely for show and public relations. They are buying quiet rather than seeking clear victory,” Mr. Lieberman said.

As of Saturday night, Mr. Netanyahu had yet to make any public remarks on the attack, although his office had issued statements denying several Israeli news media reports purporting to provide details of the strike.

A handful of politicians — including ones who rarely align with Mr. Netanyahu — did suggest that they agreed with the government’s strategy. Yair Golan, a left-wing politician and retired general, said the Israeli response had most likely damaged Iran’s military capabilities “without dragging us into an inevitable war of attrition.”

“It seems that people are hopeful that soon the situation will be back to normal,” he told The New York Times when reached by telephone.

“The vibe is not normal, though, at the moment,” he said. “People are experiencing different emotions: Some are worried, some indifferent and some are even happy, because they believe that Israel attacks will humble the regime a bit.”

Soheil, like other Iranians reached by The Times on Saturday, asked not to be identified by his full name for fear of retribution.

Iranian officials and the state news media played down the Israeli attack, calling the damage “limited” and claiming that Iran’s air defense had intercepted the strikes.

Israel did not strike sensitive sites related to Iran’s nuclear program or oil production facilities in retaliation for the large barrage of ballistic missiles that Iran fired at Israel this month. And while the attack marked a new escalation between the two archrivals, it appeared to be calibrated to stop short of all-out war.

After the attack was completed, Iran did not immediately threaten to retaliate, but it did say that it had the right to do so.

On state television on Saturday, reporters around Tehran, the nation’s capital, cheerfully proclaimed that all was well. Live shots showed a vegetable market and morning rush-hour traffic.

But for some residents, it was a night of little sleep and high anxiety as the sounds of explosions kept them up.

Maryam Naraghi, an Iranian journalist, said she had heard “the sound of bombs and explosions” from her home in Tehran.

Houri, a 42-year-old mother of two in Tehran, said in a telephone interview that after a night of loud explosions and consoling her children, she was anxious about what lay ahead for Iranians, many of them having grown weary of conflict and years of economic hardship.

She said her husband had stayed glued to satellite television and social media all night for updates on the attacks because Iran’s state news media offered little information.

Yashar Soltani, a journalist, said he had woken up in Tehran to the sounds of an attack that seemed to be nearby.

“I saw very big lights in the sky,” he said.

The attack on military bases and other targets in Ilam, Khuzestan and Tehran Provinces lasted only a few hours and was over by about 5 a.m., Israeli officials said.

As the sun rose on Saturday, people in Iran tried to go on with their day as usual, hoping that a wider war could be avoided.

Shadi, a 41-year-old living in Tehran, said she had not heard any of the explosions overnight.

“We people of Iran are victims of all these political games,” she said. “We have experienced so much that we all have become somehow numb.”

Farnaz Fassihi contributed reporting.

If it does not, it risks looking weak to those same allies, as well as to more aggressive and powerful voices at home.

Iran is already in the middle of a regional war. Since the Hamas-led attack on Oct. 7, 2023, Israel has moved swiftly to damage the militant group in Gaza and other Iranian proxies, including Hezbollah, the Houthis and its allies in Syria and Iraq.

These groups represent Iran’s “forward defense” against Israel, the heart of the nation’s deterrence. They have been badly weakened by the Israeli military’s tough response since Oct. 7, which weakens Iran, too, and makes it more vulnerable.

Iranian officials have made it clear that they do not want a direct war with Israel. They want to preserve their allies, the so-called ring of fire around Israel.

After Israel struck Iran, Tehran on Saturday publicly played down the effect of the attack and showed ordinary programming on television. It did not immediately vow a major retaliation, but simply restated its right to do so.

Adding to its reticence, Iran faces enormous economic problems, making it wary of an extended and costly war with Israel. It has been heavily penalized by the United States and Europe over its nuclear program, forcing it to move ever closer to Russia and China.

The Islamic regime is also dealing with serious domestic dissent over rising prices and its harsh rule, which play into any calculation for retaliation. The regime is both committed to the destruction of Israel, but also to preserving its power in a sophisticated country in which it is increasingly unpopular.

That is one reason, analysts believe, the supreme leader, Ayatollah Ali Khamenei, allowed the election of a more moderate president, Masoud Pezeshkian, after the harder-line Ebrahim Raisi died in a helicopter crash. Against the backdrop of domestic unrest, Mr. Pezeshkian has pushed for new talks on Iran’s nuclear program in return for a lifting of economic sanctions, outreach that most likely could take place only with the permission of the supreme leader.

The nuclear program is its own dilemma. The damage to allies over the past year, as well as its clear technical and military weakness compared with Israel, will put more pressure on Iran to advance its nuclear program and go for a bomb.

Iran is already within weeks of creating bomb-quality uranium, and there are strong voices in Iran arguing that the best deterrent against Israel and the United States is to have nuclear weapons, as Israel itself possesses. But Iran also knows that a series of American presidents — including Donald J. Trump, who is running neck and neck against Vice President Kamala Harris in the U.S. presidential race — have vowed to prevent Iran from attaining an operational nuclear weapon.

Complicating matters, a quiet battle has emerged over the succession of Ayatollah Khamenei, who is 85. With Mr. Raisi gone, there is internal disquiet over the possibility that Ayatollah Khamenei’s second son, Mojtaba, 55, might succeed him. The powerful Islamic Revolutionary Guards Corps will have an important say and is considered more willing to confront Israel.

Whatever Iran’s ultimate calculation, hoping to avoid a larger war does not mean it can.

Both Israel and Iran are eager to restore the so-called deterrence effect that they believe comes with retaliatory strikes. As they see it, it enhances their ability to intimidate each other and allows them to limit each other’s power, in what Jeremy Shapiro, a former American diplomat, has called their “geopolitical manhood.”

This past week, as might be expected, Iran’s foreign minister, Abbas Araghchi, said that “in the event of an Israeli attack, the shape of our response will be proportionate and calculated.”

These back-and-forth attacks, however carefully calibrated, can easily spill over into wider violence if a hospital or a school is hit, even by accident, and causes significant civilian casualties.

As Daniel C. Kurtzer and Aaron David Miller wrote this week in Foreign Policy, “a spiraling tit for tat would likely prompt the Israelis to expand their target set, at a minimum, to include economic infrastructure.” From there, they added, “it’s certainly possible to imagine a regional escalation, including Iranian attacks on Saudi oil infrastructure.”

But Iran may also choose to heed American and British advice to call an end to this round of retaliations as negotiations for cease-fires in Gaza and Lebanon gather pace.

Ali Vaez, the Iran project director for the International Crisis Group, said on X that Israel’s response was “considerably more robust” than the one in April.

Israel struck Iranian air defenses and missile manufacturing sites in three provinces, while also attacking targets in Iraq and Syria, according to Israel officials. But it avoided key infrastructure, energy and nuclear sites.

The key question, Mr. Vaez said, was simple: “Whether Tehran will absorb the hit and try to draw a line under this exchange or up the ante again with a counter-response.”

For Iran, the argument for climbing down the escalatory ladder is a strong one. But there are powerful voices like the Islamic Revolutionary Guards Corps, which regularly press for a more aggressive response.

The desire for Washington and Israel, too, is that the conflict with Iran “becomes once again a shadow war and not an overt war,” said David Makovsky, a fellow at the Washington Institute for Near East Policy. “In today’s world that would be an achievement. You don’t end the enmity but bring it under control.”

Sanam Vakil, the director of the Middle East Program at Chatham House, said that the U.S. presidential election in November is also a factor. “If Iran wants to avoid a broader escalatory conflict in advance of the uncertain U.S. election, it must take the hit and play a longer strategic game focused on diplomatic outreach to the region and openings should they emerge from the West,” she said.

By playing down the effect of the strike and pressing for a cease-fire, she said, “Iran will try to turn the tables on Israel and translate its military weakness into diplomatic openings.”