“We are encouraged that partner nations see the value in taking responsibility for the appropriate disposition of their citizens who chose to travel to Syria and fight ISIS,” said Garrett Marquis, a spokesman for the White House’s National Security Council, who declined to address specific countries.

Additionally, reports last month indicated that France is close to deciding whether to bring back about 130 of its detained citizens, including men, women and children. Other European countries with large numbers of detained citizens, including Germany and Belgium, are said to be closely watching how Paris will decide, with an eye toward echoing it.

In a statement to The New York Times, France’s Ministry for Europe and Foreign Affairs made clear that the withdrawal of American forces from Syria had forced it to deal with the detainees.

“In light of developments in the military situation in northeastern Syria and American decisions, and in order to ensure the security of French people, we are exploring all options in order to prevent these potentially dangerous individuals from escaping or dispersing,” the statement said.

Christopher P. Costa, a former National Security Council senior director for counterterrorism in the Trump administration, said the new willingness by nations is a positive sign for a dilemma that has few good answers.

“States don’t always think that this president is predictable in many ways, so if we can enjoy countries taking on ownership of detainees, that is a good outcome of accelerating withdrawal of U.S. forces,” said Mr. Costa, now the head of the International Spy Museum in Washington.

Countries have different reasons for their reluctance to take back Islamic State detainees.

Most are rooted in security concerns about people who may be difficult to successfully prosecute and imprison with lengthy sentences. Even those who pose little or no security risks may be hard to reintegrate into society because of their ideology or wartime experiences, and children who had been part of ISIS through no fault of their own are likely to be stigmatized.