More than 100 Islamic State prisoners have escaped in Syria: US envoy

More than 100 prisoners of the Islamic State extremist movement have escaped in Syria in the chaos since Turkey's incursion, a senior US official said Wednesday.

"We would say the number is now over 100. We do not know where they are," James Jeffrey, the State Department pointman on Syria, told the House Foreign Affairs Committee when asked about the detainees.

Turkey launched a military operation in Syria after President Donald Trump agreed to pull US troops who were allied with the Syrian Democratic Forces, the Kurdish-led group that bore the brunt of the fight against the Islamic State group.

Jeffrey said that the Kurdish fighters were still guarding prisoners from the extremist group, despite their warnings that they will need to devote resources to fight Turkey instead.

"Almost all of the prisons that the SDF were guarding are still secured. The SDF still has people there," Jeffrey said.

"We are monitoring that as best we can. We still have people in Syria working with the SDF and one of those priorities is these prisons," he said.

The Kurdish fighters have pulled out of a key border area as part of a US-brokered agreement with Turkey to end the offensive.

Turkey links the Syrian Kurdish fighters to PKK separatists at home, who are considered a terrorist group by the United States and the European Union.