The senior American diplomat slipped quietly into Belarus, a police state run by a strongman reviled for decades in the West, traveling by car across the border for meetings with President Aleksandr G. Lukashenko and the head of his KGB security apparatus.

It was Mr. Lukashenko’s first meeting with a senior State Department official in five years, and the start of what could be a highly consequential thawing of frozen relations between the United States and Russia’s closest ally.

The below-the-radar American visit to Minsk, the Belarusian capital, on Wednesday came just a day after President Trump had a long telephone call with President Vladimir V. Putin of Russia. Both events signaled Washington’s departure from a yearslong policy of trying to isolate leaders out of favor in the West because of their repressive policies and the war in Ukraine.

After talks with Mr. Lukashenko, Christopher W. Smith, a deputy assistant secretary of state, and two other American officials drove to a village near the border with Lithuania. There, courtesy of the Belarusian KGB, three people who had been jailed — an American and two Belarusian political prisoners — were waiting to be picked up.

As darkness fell, the Americans and the freed prisoners drove back across the border to Vilnius, the Lithuanian capital. Speaking outside the U.S. Embassy there on Wednesday evening, Mr. Smith hailed the successful completion of what he called “a special operation,” describing the prisoners’ release as a “huge win and a response to President Trump’s peace through strength agenda.”

The next step, Mr. Smith told a gathering of Western diplomats on Thursday in Vilnius, according to people who attended, is a possible grand bargain under which Mr. Lukashenko would release a slew of political prisoners, including prominent ones. In return, the United States would relax sanctions on Belarusian banks and exports of potash, a key ingredient in fertilizer, of which Belarus is a major producer.

The people who relayed Mr. Smith’s account of his talks in Minsk spoke on the condition of anonymity to discuss a confidential meeting. Mr. Smith himself has not publicly disclosed whom he met with or what was discussed, and the State Department did not respond to questions about those details.

Belarus, which usually gloats over any sign that it is breaking out of its isolation, has also been mostly silent, though an anchor on state television, Igor Tur, introduced a note of mystery, suggesting that Mr. Smith was not the real leader of the American delegation and that a more senior official also took part.

Franak Viacorka, the chief of staff to the exiled opposition leader Svetlana Tikhanovskaya, who has long called for toughening of sanctions, said: “We are very grateful to President Trump that he managed to move things forward.” But, he added, sanctions should be eased only when “Lukashenko stops repression and new arrests” and “releases all political prisoners, including top figures.”

Viasna, a human rights group that keeps a tally of political prisoners in Belarus, put their number this week at 1,226. Mr. Lukashenko has in recent months released more than 200 of them, including two Americans set free since Mr. Trump took office, but opposition activists say that even more people have been arrested during the same period.

Tatyana Khomich, a sister of one of Belarus’s most prominent political prisoners, Maria Kolesnikova, welcomed the American outreach to Mr. Lukashenko. “The past pressure strategy has failed to release political prisoners, halt repression or change the regime’s behavior,” she said.

Mr. Smith also steered Belarus policy during the Biden administration, and started tentative discussions last year with U.S. allies about easing sanctions, but until this week he had never traveled to Minsk to meet Mr. Lukashenko.

That “direct diplomatic approach could yield concrete results, including the release of individual prisoners or even a broader amnesty,” Ms. Khomich said, while loosening Belarus’s dependence on Russia and “preserving some leverage for the U.S. and E.U.”

An American-led drive to isolate and bankrupt Mr. Lukashenko under the Biden administration produced a raft of Western penalties. The sanctions on potash cut an important economic lifeline for the Belarusian ruler but handed a windfall to Russia, another big producer, as global prices spiked. Some Belarusian potash continued to reach global markets via Russia, instead of by the previous, cheaper route through Lithuania.

Artyom Shraibman, a political analyst who fled Belarus after a brutal crackdown on protests in 2020, said Western sanctions had little impact because of Russia’s expansive support for Mr. Lukashenko. But a release of prisoners in return for relaxing sanctions, he said, would “mean they have finally been used with some effect.”

“This would be definitely a positive development for the prisoners themselves, their families — and potentially for solving broader issues of the relationship” between Belarus and the West, said Mr. Schraibman, a nonresident scholar at the Carnegie Russia Eurasia Center.

How to deal with Mr. Lukashenko has vexed Western policymakers for decades. A master at maneuvering between East and West, and silencing his critics at home, he took power in 1994 and has won seven increasingly dubious elections in a row, most recently in January, when he claimed 87 percent of the vote, his biggest landslide yet.

In 2005, the U.S. secretary of state at the time, Condoleezza Rice, denounced Belarus as the “last true remaining dictatorship in the heart of Europe” — though that was before Mr. Putin consolidated his autocratic control of Russia.

Dispirited by the longevity of Mr. Lukashenko, now 70, his exiled opponents, like Mr. Putin’s, have often sought solace in rumors that he was seriously ill. But Mr. Smith, briefing Western diplomats in Vilnius, reported that Mr. Lukashenko showed no sign of ill health and seemed confident and in full control, several of those who attended said.

Beginning a decade ago, efforts to isolate Mr. Lukashenko gave way for a time to engagement, amid signs that Belarus wanted to avoid becoming too dependent on Moscow, the country’s increasingly overbearing neighbor.

While heavily reliant on Russia for deliveries of cheap oil, which he needed to keep his faltering economy afloat, Mr. Lukashenko resisted pressure from Mr. Putin to fully implement a 1990s agreement to form a “union state” that he feared would reduce Belarus to a province of Russia.

Before a presidential election in 2020, relations with Russia became so tense that Belarus jailed a challenger it described as a stalking horse for Moscow, and later arrested 33 Russians it said were mercenaries from the Kremlin-linked Wagner Group who had infiltrated the country to disrupt voting.

But the pendulum swung hard the other way after Mr. Lukashenko claimed an implausible victory over Ms. Tikhanovskaya in that election, which Western governments denounced as rigged, and huge street protests broke out in Minsk and cities across the country.

Mr. Lukashenko appealed to Mr. Putin, who rushed in security advisers to help restore control. Vicious repression followed, with mass arrests and torture of detainees.

Less than a year and a half later, Mr. Lukashenko allowed Russia to use his country as a staging ground for its full-scale invasion of Ukraine, with an abortive thrust south from Belarus toward Kyiv.

Mr. Smith, according to diplomats who attended his briefing, said the primary U.S. goal was to secure freedom for more political prisoners. He said he had asked Mr. Lukashenko whether he was ready to scale back repression and was assured that he was. Another important aim, Mr. Smith told the diplomats, is to give Mr. Lukashenko some breathing room outside Russia’s orbit of influence.

Piotr Krawczyk, a former head of Poland’s foreign intelligence service who worked with the first Trump administration on loosening Russia’s grip on Belarus, said Belarus was “part of a wider American approach toward Russia.”

The United States is “confronting Russia in Ukraine, in Africa, in the oil and gas sector, and in several other strategic areas,” he said. “Negotiating with Belarus creates additional leverage for the U.S. to signal to Russia that they should be more attentive to American arguments.”

Mr. Shraibman, the exiled analyst, said a big question now was how the Kremlin would react to any rapprochement between Belarus and the West. Many Russian officials “would likely panic at the prospect,” he said, but “there is no quick or easy way for Belarus to distance itself from Russia given Moscow’s economic dominance over the country.”

He added that it was unlikely that President Trump “has any particular interest in, understanding of or a plan for Belarus.” Even so, he said, the “Trump factor certainly creates some momentum, as everyone, including Lukashenko, tries to impress the U.S. president and compete for his attention.”

Chancellor Olaf Scholz of Germany on Saturday accused Vice President JD Vance of unacceptably interfering in his country’s imminent elections on behalf of a party that has played down the atrocities committed by the Nazis 80 years ago.

A day after Mr. Vance stunned the Munich Security Conference by telling German leaders to drop their so-called firewall and allow the hard-right Alternative for Germany, or AfD, to enter their federal government, Mr. Scholz accused Mr. Vance of effectively violating a commitment to never again allow Germany to be led by fascists who could repeat the horrors of the Holocaust.

“A commitment to ‘never again’ is not reconcilable with support for the AfD,” Mr. Scholz said at the conference on Saturday morning, in an address opening the gathering’s second day.

Mr. Scholz said the AfD had trivialized Nazi atrocities like the concentration camp at Dachau, which Mr. Vance visited on Friday. The chancellor said Germany “would not accept” suggestions from outsiders about how to run its democracy — or directives to work with such a party.

“That is not done, certainly not among friends and allies,” Mr. Scholz said. “Where our democracy goes from here is for us to decide.”

Attendees at Mr. Vance’s speech had been expecting to hear details of the Trump administration’s plans for Ukraine peace talks and NATO defense policies. On Saturday, President Volodymyr Zelensky of Ukraine himself put the focus on the Ukraine war in his remarks, starkly laying out the threat from Russia’s battle-hardened military and making an impassioned appeal for Europeans to take their security into their own hands, including by forming an “Army of Europe” that would supplement U.S. power on the continent.

His speech drew standing ovations, in contrast to Mr. Vance’s speech the day before.

Mr. Scholz’s comments underscored a growing unease among Europe’s leaders about their relationship with the United States, and their own domestic politics. They came as leaders scrambled at the summit to formulate a response to President Trump’s sudden shift in Ukraine policy — and the possibility that he could cut the continent out of negotiations.

Just a few days before Mr. Vance’s remarks, Mr. Trump threatened to impose new tariffs on virtually every country the United States trades with. Then he spoke of negotiating an end to Russia’s war in Ukraine directly with President Vladimir V. Putin of Russia, leaving Europeans, including Ukraine, wondering if they would be included. Poland’s foreign minister said at the summit that President Emmanuel Macron of France had called an emergency meeting of European leaders to discuss Ukraine on Sunday.

At the same time, far-right parties across Europe have gained ground by tapping into unease over immigration, which also helped propel Mr. Trump back to power in the United States. Mr. Vance’s comments suggested that a new kind of American alliance with Europe was forming, one that bypasses the official leadership in favor of movements like Germany’s AfD and France’s National Rally.

Saturday’s sessions of the security conference were dominated by reactions, predominantly negative, to Mr. Vance’s speech — and Mr. Trump’s agenda.

Mr. Scholz was joined in his criticism by Friedrich Merz, his rival as the chancellor candidate for the conservative Christian Democrats, who polls suggest is the favorite to be Germany’s next leader.

Mr. Vance spent much of his speech on Friday scolding Europeans for what he suggested were Soviet-style restrictions on free speech across the continent. On Saturday, Mr. Merz defended Germany’s laws that prohibit particular forms of speech, including hate speech and banned Nazi slogans, including on social media.

He also suggested that Mr. Trump’s administration was suppressing speech in the United States, after it moved on Friday to kick The Associated Press out of reporting pools and off Mr. Trump’s plane because the news agency refuses to go along with Mr. Trump’s directive to change the name of the Gulf of Mexico to the Gulf of America.

“We stick to the rules which are given by our democratic institutions,” Mr. Merz said. “Free speech remains free speech and remains part of our open, democratic society. And fake news, hate speech and offenses remain subject to legal restraints and controlled by independent courts.”

“I think I should say,” he added, “that in front of the events which took place in D.C. yesterday — we would never kick out the news agency, out of the press room of our chancellor.”

Mr. Merz also criticized Mr. Trump’s tariff policy, saying that Germany wanted to reduce tariffs, not increase them, and that “we don’t believe in trade conflicts.”

The White House had no immediate comment on the remarks by Mr. Scholz and Mr. Merz.

The comments were the latest in a series of critiques of Mr. Vance’s speech from German politicians before the election next Sunday. Mr. Scholz’s Social Democrats are running third or fourth in most polls. The AfD is running second, and its chancellor candidate, Alice Weidel, met Mr. Vance on Friday in Munich.

Parts of the AfD have been classified as extremist by German intelligence. Some of its members have been convicted of violating German law against the use of Nazi slogans. Others have been arrested for trying to overthrow the federal government. So although AfD candidates have been able to win parliamentary seats, no other party has been willing to form a coalition with them to take control of the government.

That collective shunning of the AfD and other extremist parties is known as the firewall. Mr. Vance took aim at it on Friday, saying the AfD and other hard-right parties across Europe represented legitimate voter concerns about high levels of migration into European countries from the Middle East and elsewhere.

“There is no room for firewalls,” Mr. Vance said.

The vice president also called restrictions on free speech a greater threat to Europe than military aggression from Russia or China.

Mr. Scholz chided Mr. Vance for that focus in a question-and-answer session after his speech. He was asked by Zanny Minton Beddoes, the editor in chief of The Economist, if Mr. Vance had made any points in his speech worth reflecting on.

“You mean all these very relevant discussions about Ukraine and security in Europe?” Mr. Scholz said, drawing laughter from the audience.

Then he addressed Mr. Vance’s critique of European speech restrictions directly.

“We should be very clear that free speech in Europe means that you are not attacking others in ways that are against legislation and laws we have in our country,” Mr. Scholz said. “And that’s the case. There is no difference between the digital world and the analog world to say it like this. And we have to be very clear that hate and all this, which is so bad for our societies, should be not the reality of public debate.”

Mr. Zelensky, in his remarks, focused on the question of European defense. He reiterated his position that the United States would be pivotal in securing any cease-fire in Ukraine but that it would need Europe to also step up. He pointed to what he said were intelligence warnings of Russian plans to conduct military exercises in Belarus next summer. He noted that Russia had invaded Ukraine after deploying troops to Belarus under the guise of exercises.

“Europe just needs to come together and start acting in a way that no one can say ‘No’ to Europe, boss it around, or treat it like a pushover,” Mr. Zelensky said.

Mr. Trump has said he wanted access to minerals in Ukraine worth half a trillion dollars in exchange for continued military support; Treasury Secretary Scott Bessent opened talks on that issue in Kyiv earlier this week. “We are still talking,” Mr. Zelensky said on Saturday.

In a conversation with the CNN anchor Christiane Amanpour after his speech, Mr. Zelensky also said that Ukraine needed to be at the table at any cease-fire talks, and he asked to meet with Mr. Trump before any meeting that Mr. Trump has with President Vladimir V. Putin of Russia.

“It’s up to them, they can discuss anything they want, but not Ukraine without Ukraine,” he said.