BEIRUT • The United States’ Kurdish allies had been gearing up for a new fight for weeks, digging trenches and defense tunnels in northeastern Syria in preparation for an offensive Turkey’s president warned was imminent.

On the ground, U.S. troops were bringing in reinforcements through the border with Iraq, beefing up patrols and observation points to prevent friction between the Turks and their Kurdish partners.

Then, in a surprise announcement, President Donald Trump declared he was pulling all 2,000 U.S. troops out of Syria, declaring the IS group had been vanquished. The move, conveyed in a tweet Wednesday, plunged the volatile region into profound uncertainty, leaving America’s only allies in Syria in the lurch.

The U.S. forces “were as surprised as we were” by the White House decision, said Mustafa Bali, spokesman for the Kurdish-led Syrian Democratic Forces.

A quick and unplanned withdrawal of American forces opens the door for major turmoil as various groups rush to fill the political and security vacuum, including Russia, Iran and President Bashar Assad’s government.

Experts warn the Islamic State group, fighting to hang on to its last pockets in Syria, would soon find its way back.

“A full withdrawal sends the wrong signal, one that also will be heard by other counterterrorism partners far from Syria,” said William F. Wechsler, senior adviser at the Atlantic Council.

U.S-backed Syrian Manbij Military Council stands next to a U.S. humvee at a U.S. troop’s outpost on a road north of Manbij, Syria.

the associated press