German Defense Minister Ursula von der Leyen and acting secretary of defense Patrick Shanahan speak at the annual Munich Security Conference on Friday. (Andreas Gebert/Reuters)

The Trump administration is pressing allies to commit to remaining in Syria after American forces depart, a sign of how President Trump’s decision to abruptly end the U.S. military mission there has unleashed a scramble to cement security gains.

Acting defense secretary Patrick Shanahan on Friday met at a security conference in Munich with counterparts from nations that have troops deployed in Iraq and Syria, part of his first foreign tour since becoming Pentagon chief last month.

“While the time for U.S. troops on the ground in northeast Syria winds down, the United States remains committed to our coalition’s cause, the permanent defeat of ISIS,” Shanahan told reporters after the talks, characterizing Trump’s decision to withdraw all 2,000 U.S. troops in coming months as a “tactical change.”

Shanahan, speaking on the sidelines of the conference, said he is looking for other nations to step up as the United States concludes its ground mission by April. “I look forward to working together to put thoughts and plans into concrete action,” he said.

But European allies have expressed skepticism about assuming responsibility for a risky and politically fraught campaign, especially given the U.S. exit plans.

“At this point, we need to ask ourselves why U.S. allies would want to invest doubly in a mission whose future looks so deeply uncertain,” said Charles Lister, a senior fellow at the Middle East Institute, a Washington think tank. “The risk involved here, being left out in the open, looks just too big for it to be justifiable in allied capitals.”

The closed-door talks, which also included Turkey, Germany, Iraq and other nations, occurred as U.S. diplomats and generals race to assemble a plan to avert an Islamic State resurgence, as well as a battle between Turkish troops and a Kurdish-dominated local force that has been the chief U.S. partner in Syria. Turkey regards that group, the Syrian Democratic Forces, as a threat to its security.

Trump’s withdrawal announcement in December surprised many U.S. officials, upending Pentagon plans for an ongoing campaign against militant strongholds in eastern Syria and rattling American allies that have been fighting alongside Washington since the war against the Islamic State began. Shanahan’s predecessor, retired Marine general Jim Mattis, resigned shortly afterward.

Officials said the Munich discussion was not intended to secure troop commitments from allies but to address requirements for the period after American forces withdraw.

“There’s a tremendous desire to have a security arrangement or mechanism that doesn’t result in a security vacuum,” a senior U.S. defense official said, speaking on the condition of anonymity to characterize coalition discussions. “What that is is still being developed, and frankly it’s an area where ministers have different views.”

The official said France had indicated it would not keep forces in Syria after the U.S. departure. Britain has also had a Special Operations presence there. A British official declined to provide details about military plans.

In a CNN interview aired Friday, the top U.S. general for the Middle East, Joseph Votel, said he did not support Trump’s withdrawal decision. Many military officials fear that the Islamic State, which has continued to launch attacks in areas it abandoned in Iraq and Syria, will strengthen underground and potentially pose a renewed threat.

Trump, speaking in Washington on Friday, hinted that he was preparing to announce the completion of operations in areas of Syria that were held by the Islamic State.

It was not immediately clear whether a continued Western military mission in Syria, if it were to occur, would focus on training a local stabilization force or on preventing a Turkish-Kurdish confrontation in a proposed buffer zone in northern Syria near the Turkish border.

Even some of Trump’s closest allies have expressed concern about his Syria plan. In a panel discussion at the same conference, Sen. Lindsey O. Graham (R-S.C.) encouraged U.S. allies in Syria to remain there even after American forces depart. The military campaign against the Islamic State, Graham said, has been “the best return on investment in the history of warfare.”

But he argued that a preemptive withdrawal of Western forces could result in a resurgence of the militant group, just as the organization regenerated after the U.S. exit from Iraq. Graham read from a list of Islamic State attacks in Europe and the United States in recent years. “Does it matter what happens over there?” he asked. “Hell yeah, it matters.”

Graham, who said he spoke to the president just before he took the stage, has said that an abrupt departure could also benefit Iran. He invoked the name of his former colleague and fellow defense hawk, the late senator John McCain, in asking U.S. allies to say yes when Trump asks them to leave troops in Syria.

But the initial European response was questioning, at best. The United States, former Swedish prime minister Carl Bildt noted, was asking European forces to stay in a country where Trump himself had argued there was only “death and sand.”

“Not an easy sell,” Bildt remarked on Twitter.

In the ministerial talks, foreign officials did not voice concerns about the departure plan, the defense official said, suggesting that allies have moved beyond seeking to steer Washington in a different direction. The discussions also included James Jeffrey, Washington’s special envoy for the anti-Islamic State coalition.

“The conversation was much more about what do we do when the United States withdraws and less about fighting the proposition of it,” the official said. “We are very clear in all these discussions . . . that we have an order from the president and we are withdrawing, period, dot. And that’s it.”

Karen DeYoung in Washington contributed to this report.