Senior American diplomats traveled through Damascus, the Syrian capital, on Friday to meet with militias controlling the country and with civil society groups, and to look for signs of the journalist Austin Tice and other missing U.S. citizens, the State Department said.

They are the first American diplomats to enter Damascus since the crumbling of the old government, and they aim to help shape the political landscape of Syria after the rapid fall this month of Bashar al-Assad, the longtime autocratic leader. The United States broke off diplomatic ties with Syria in 2012, the year after Mr. al-Assad ordered his forces to carry out mass atrocities during the country’s civil war.

The visit represents a tentative step toward engagement in Syria, a nation in which U.S. policy in recent years has usually involved the military, not diplomacy. The Biden administration has been in contact with militia leaders but has wrestled with how to directly engage, in part because the United States has designated the lead rebel group, Hayat Tahrir al-Sham, as terrorists.

The visit was the latest in a flurry of meetings between rebel leaders and Western officials looking to gradually open channels to the new Syrian authorities. Since Mr. al-Assad’s ouster this month, diplomats from Britain, France, Germany, Switzerland and elsewhere have come to Damascus. Qatar and Turkey are also in the process of reopening their embassies there.

The diplomacy comes during a realignment across the Middle East, where Syria is a major power and stood for decades as an emblem of Arab rule by a single family, one opposed in wartime by most Syrians. At least six foreign militaries were involved in the country’s nearly 14-year civil war, including Iran, Russia and the United States.

The U.S. diplomats “will be engaging directly with the Syrian people, including members of civil society, activists, members of different communities and other Syrian voices about their vision for the future of their country and how the United States can help support them,” the State Department said in a statement.

The officials are Barbara Leaf, the assistant secretary of state for Near Eastern affairs; Roger D. Carstens, the special presidential envoy for hostage affairs; and Daniel Rubinstein, the new special adviser on Syria.

The agency said the diplomats planned to discuss with Hayat Tahrir al-Sham the “transition principles” that American, Arab and Turkish officials agreed on at a meeting last weekend in Aqaba, Jordan. American officials have emphasized that groups in Syria must build an inclusive process for governance and fairly treat ethnic and religious minorities in the country, including Christians. The U.S. diplomats also planned to meet with civil society groups on Friday.

A news conference with the American officials that was scheduled to take place at the Four Seasons hotel in Damascus on Friday afternoon was canceled at the last minute because of “security concerns,” said Rana Hassan, a State Department official.

The leader of Hayat Tahrir al-Sham, Ahmed al-Shara, formerly known by his nom de guerre, Abu Mohammad al-Jolani, has said in interviews that his group plans to have an inclusive process and does not seek to harm non-Muslims in Syria. The group is conservative and follows tenets of political Islam, but it broke from Al Qaeda and the Islamic State years ago, and has even fought them. The rebel group has administered much of Syria’s opposition-held Idlib Province since 2017.

Officials within the group have laid out an ambitious plan for establishing a new government in Syria, and rebel leaders have assumed key government positions to oversee a period of transition until March 1, 2025. After that point, rebel leaders say, a caretaker government is to be installed in consultation with Syrians of all backgrounds, and a committee to create a new Syrian Constitution will be established.

It is unclear how the American diplomats would engage with Mr. al-Shara. He and other rebel leaders have urged the United States to drop the terrorist designation, while U.S. officials have said they are watching the group’s actions closely.

Robert Ford, the former U.S. ambassador to Syria, said in an interview with The New York Times this month that the Biden administration should consider removing Hayat Tahrir al-Sham from the list of terrorist organizations. While governing Idlib Province, he said, the group has shown a tolerance for Christians and allowed them to rebuild churches. Mr. Ford had pushed President Barack Obama to put a precursor of the group on the terrorist list.

The Biden administration has also found Hayat Tahrir al-Sham willing to help in the search for Mr. Tice, who was abducted in Damascus in 2012, and has given the group a list of former Assad government officials who might have knowledge of him. President Biden has said he believes that Mr. Tice is still alive and in Syria.

The process of taking groups off various official terrorist lists in Washington can take months or years because of the web of agencies involved and the potential political costs to leaders making that decision. If Mr. Biden or President-elect Donald J. Trump, once he is in office again, were to ask the agencies to move in that direction, there would likely be months of research into the groups by each agency. That would be followed by debates among agencies and within the White House and with members of Congress, where lawmakers could raise objections.

The State Department maintains a list of foreign terrorist organizations. The Treasury Department also has an overlapping list of global terrorists, and both agencies have sanctions power. In addition, the United Nations has a sanctions list that the United States abides by, and Hayat Tahrir al-Sham is on the list. Russia, as a pro-Assad member of the United Nations Security Council, would likely argue to keep the group on the list.

The toppling of Mr. al-Assad’s government has also shifted Syria’s other diplomatic ties. It sharply diminishes Iran’s influence in the region, depriving it of a key Arab ally that for decades was critical to its defense strategy. Whether Russia will be able to maintain its military bases in western Syria, which have been crucial to its ability to project power in the Middle East, remains unclear.

Turkey has emerged as a winner, with more influence than ever over the rebels who now control most of Syria and who have long benefited from Turkish assistance.

On Friday, Turkish officials said they were in touch with Mr. al- Shara to assist in the country’s process of creating a new Constitution, pledged to assist the new government with its energy needs and called for increased efforts to destroy “terrorist” groups within Syria, like the Islamic State and Kurdish fighters.

For years, the Kurdish-led forces, who control northeastern Syria, have been America’s most reliable partner in Syria, liberating cities seized by the Islamic State. But Turkey has long seen the Kurdish forces in Syria as an enemy, allied with the separatist Kurdistan Workers’ Party, or P.K.K., in Turkey. That group has fought the Turkish state for decades and is considered a terrorist group by Turkey and the United States.

President-elect Donald J. Trump’s threats of tariffs on allies and adversaries alike have unsettled companies and governments across Europe, setting off a scramble for what they fear could be a trans-Atlantic trade war.

Their nascent plans, including a closely guarded effort at the top levels of the European Commission, appear to be more proactive than what they were the first time Mr. Trump took office. But any attempt to form a united front on trade could be hampered by the sclerotic politics across much of Europe.

The French and German governments both collapsed this month. Austria and Belgium are struggling to form governing coalitions long after their most recent elections.

And no clear consensus has emerged on how to respond to whatever Mr. Trump might have in store. Divisions are already emerging between officials who favor a strategy of retaliation if he tries to impose new taxes on European exports and those who favor negotiation.

In a post on Truth Social early Friday, Mr. Trump said he had “told the European Union that they must make up their tremendous deficit with the United States by the large scale purchase of our oil and gas. Otherwise, it is TARIFFS all the way!!!”