The move was confirmed by the U.S. military, which said in a statement that U.S. forces in the region had "paused all partnered operations" against Islamic State in Syria.

Turkey has ramped up its shelling and air strikes on northern Syria in recent weeks and is preparing a ground invasion against Syrian Kurdish fighters that it dubs terrorists but who make up the bulk of the SDF.

The SDF has long warned that fighting off a new Turkish incursion would divert resources from protecting a prison holding IS fighters or fighting IS sleeper cells still waging hit-and-run attacks in Syria.

SDF spokesman Aram Henna told Reuters that "all coordination and joint counter-terrorism operations" with the U.S.-led coalition battling remnants of the Islamic State in Syria as well as "all the joint special operations we were carrying out regularly" had been halted.

The Turkish bombardment - using both long-range weapons and air strikes - has frustrated its NATO ally Washington.

U.S. Defense Secretary Lloyd Austin told his Turkish counterpart on Wednesday that the United States was in "strong opposition to a new Turkish military operation in Syria." Austin also said Turkish raids had directly threatened the safety of U.S. personnel.

White House spokesman John Kirby on Friday echoed those remarks, telling reporters that while the United States backs Turkey's ability to defend itself in Turkey, "there's lots of reasons why these operations give us concern," including the potential harm to civilians and Americans in that part of Syria.

"We also don't want to see anything that would affect our ability to continue to put the pressure on ISIS and to affect our partnership with the SDF," Kirby told reporters in a briefing, adding that previous Turkish operations have made the SDF "less willing to continue to contribute to counter-ISIS" operations.

The U.S.-led coalition has backed the SDF with air strikes, military equipment and advisers since 2017, first helping it wrest back territory from IS and then supporting clearing operations against jihadist sleeper cells.

Sheikhmous Ahmed, the head of the displacement department in Syria's northeast, told Reuters that Turkish raids in late November had disrupted operations in and around al-Hol, a detention camp where women and children affiliated to IS fighters are held.

He said humanitarian operations were suspended for several days and that some minors affiliated to IS tried to escape but were caught.

A Western source briefed on the matter said there had been "some worrying movement" in the area where foreign IS-linked women and children were held.

But a spokesperson for U.S. Central Command said the SDF continued to "conduct patrols and maintain security at the al-Hol displaced persons camp and the detention facilities."

SDF head Mazloum Abdi told Reuters earlier this week that he wanted to hear a stronger message from Washington in response to unprecedented Turkish deployments along the border.

"We are still nervous. We need stronger, more solid statements to stop Turkey," he said.

Reporter's code: 50101