Syrian government troops backed by Russian forces have sent extra troops towards the city of Manbij in coordination with the militia that controls it, a militia spokesman said, as Turkish-backed Syrian rebels said they were preparing to attack it.
The deployment was coordinated with the U.S.-backed militia in Manbij, the spokesman for the Manbij Military Council said.
It is part of the wider buildup of forces in the area.
"The battle will soon start," Major Youssef Hamoud, spokesman for the National Army, the main Turkish-backed rebel force in the area, told Reuters.
"What we see on the front now is reinforcements to all forces to reach full preparedness for the battle."
President Donald Trump's plan to withdraw U.S. troops from Syria has triggered alarm among the largely Kurdish-led Syrian Democratic Forces (SDF).
They have partnered with Washington in the war against Islamic State and now fear the U.S. move will open the way for Turkey to launch a long-threatened attack against them.
"The Russian army has restored the Syrian-Russian coordination centre to Arima village to the west of Manbij city, after its withdrawal from there a while ago," said Sharfan Darwish, the spokesman for the Manbij Military Council.
Manbij was seized in 2016 from Islamic State by Syrian militia allied to the SDF, which control roughly a quarter of Syria. Its capture was a milestone in the U.S.-backed campaign against Islamic State.
In June, the United States and Turkey reached an agreement that would see the Syrian Kurdish YPG militia ousted from the town, but Turkey says its implementation has been delayed. In November Turkish and U.S. troops began joint patrols in the region.
Turkey is determined to cross to the east of the Euphrates river in northern Syria as soon as possible, Ankara's foreign minister was quoted as saying on Tuesday.
Ankara regards the YPG as terrorists and has been infuriated by U.S. support for the group in the fight against Islamic State.
Trump's abrupt decision to pull troops out of Syria has handed the fight against Islamic State over to Turkey - and effectively given Ankara the green light to push into remaining Kurdish-controlled areas in northern Syria.
