Trump has previously unnerved allies by announcing a unilateral pullout of U.S. forces in Syria | Brendan Smialowski/AFP via Getty Images Trump threatens to release ISIS fighters if EU doesn’t take them US president’s tweet draws confusion and some outrage from European officials.

MUNICH — U.S. President Donald Trump threatened to release 800 ISIS fighters captured in Syria unless European allies agree to accept them and put them on trial.

"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 wrote.

"The alternative is not a good one in that we will be forced to release them."

Trump’s threat, characteristically in a tweet, drew confusion and some outrage from European officials and security experts gathered Sunday at the annual Munich Security Conference in Germany.

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. The Caliphate is ready to fall. The alternative is not a good one in that we will be forced to release them........ — Donald J. Trump (@realDonaldTrump) February 17, 2019

Trump has previously unnerved allies by announcing a unilateral pullout of U.S. forces in Syria and in recent days Trump allies, including Vice President Mike Pence and Senator Lindsey Graham, have said during the Munich conference that the president expected European forces to take over for the withdrawing American troops.

Spanish Foreign Minister Josep Borrell was among the European officials to quickly say they have no intention of meeting Trump’s demand for additional troops.

“Requests between countries aren’t made in press releases or conference comments,” Borrell told reporters in Munich on Saturday. “Spain and the majority of countries aren’t prepared to step in for the U.S. after a withdrawal that was decided in a unilateral way, by surprise.”

Trump’s demand regarding the 800 fighters complicates an already tense debate about what European countries should do regarding combatants who have been captured fighting for the Islamic State, some of whom are European citizens.