The move occurred after the Kurdish YPG militia urged Damascus to protect the town, where U.S. forces operate, from the threat of a Turkish offensive.

Manbij has emerged as a focal point of new tensions after U.S. President Donald Trump’s decision to withdraw U.S. forces whose presence has effectively deterred Turkey.

After a Syrian army announcement declaring government troops had entered Manbij, Turkey-backed Syrian rebels stationed in nearby territory said they had begun moving together with Turkish forces toward the town in readiness for “the start of military operations to liberate” it, Reuters reported.

A witness said convoys of Turkey-backed insurgents, with armored vehicles and machine guns, were moving toward the frontline with the town.

The Syrian Observatory for Human Rights, a UK-based monitoring group, said the Syrian government forces had entered a strip of territory at the edge of Manbij, not inside the town itself, creating a barrier with Turkey-backed fighters nearby.

Manbij, where U.S. troops have a military base, is held by a local militia allied to the YPG which Turkey deems a security threat.

A U.S. official, speaking on the condition of anonymity, told Reuters that U.S. troops had not changed their positions in Manbij and dozens still remained. The official said they had not seen Syrian military forces inside Manbij but rather on the outskirts of the city.

The U.S.-led coalition against Islamic State said that “despite incorrect information about changes to military forces in the city of Manbij, Syria, (the coalition) has seen no indication that these claims are true”.

Turkish President Tayyip Erdogan, who has vowed to crush the YPG, said Turkish officials would visit Russia on Saturday and discuss Syria. He indicated Turkey was not in a hurry to launch an offensive.

Trump’s abrupt decision to withdraw troops from Syria has alarmed the Kurdish-led fighters who have fought Islamic State alongside them for years.

Kurdish leaders are scrambling for a strategy to protect their region stretching across the north and east, where the presence of some 2,000 U.S. troops has so far deterred Turkey.

A deployment of Syrian government forces, backed by Russia, would complicate any offensive by Turkey and its Syrian rebel proxies.

U.S. military support for the Kurdish fighters has infuriated Turkey, which sees the YPG as an extension of the PKK movement that has been waging an insurgency inside Turkey for decades.

The YPG said on Friday its fighters had withdrawn from Manbij before to fight Islamic State elsewhere.

“We invite the Syrian government, to which we belong, as people, land and borders, to send its armed forces to take over these positions and protect Manbij in the face of Turkish threats,” it said.

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