MUNICH -- President Donald Trump threatened Sunday to release hundreds of Islamic State fighters being held in Syria if allies in Europe don't agree to take custody of the militants.

"The United States is asking Britain, France, Germany and other European allies to take back over 800 ISIS fighters that we captured in Syria and put them on trial," Trump said in a late-night tweet. "The Caliphate is ready to fall. The alternative is not a good one in that we will be forced to release them."

Trump, who intends to pull U.S. troops out of northern Syria, said the likely destination for the militants would be European countries. "The U.S. does not want to watch as these ISIS fighters permeate Europe, which is where they are expected to go," Trump said.

During the civil war in Syria, hundreds of militants flooded into the country, many coming from Europe to join ISIS' ranks. It's unclear how many of the militants Trump is referring to are actually European citizens.

Trump's comments come as global leaders wrap up three days of security talks in Munich, where the conflict in Syria was among the agenda items.

James Jeffrey, the U.S.'s special representative on Syria issues, said in Munich that the U.S. will leave northeastern Syria, but the troop pullout will not be abrupt.

"It will be an orderly step-by-step withdraw," Jeffrey said without offering a timeline.

In December, Trump called for a complete withdraw of U.S. forces in the country. And on Saturday, Vice President Mike Pence reiterated that the U.S. still plans to wind down the mission in Syria.

Still, the U.S. said it intends to keep its coalition together and wants allies to play a larger role in the broader campaign to root out ISIS elements.

Jeffrey said there are hundreds of ISIS cells scattered throughout the region. U.S. air power will remain ready to respond when needed, he said.

Trump has essentially declared victory over the group, which has been forced out of all its former strongholds in Iraq and Syria. But there remain concerns that ISIS could regroup if the U.S. pulls out. Trump said the time has come for other countries to pick up the slack.

"We do so much, and spend so much -- Time for others to step up and do the job that they are so capable of doing. We are pulling back after 100% Caliphate victory!," Trump tweeted.

This article is written by John Vandiver from Stars and Stripes and was legally licensed via the Tribune Content Agency through the NewsCred publisher network. Please direct all licensing questions to legal@newscred.com.