BEIRUT, Lebanon — Syria’s most powerful Kurdish militia has called on the Assad government to send its forces to protect against an attack by Turkey, the first sign of shifting political alliances in eastern Syria since President Trump announced that he would withdraw American troops.
At issue is an expanse of territory in the country’s north and east that the United States, in partnership with local Kurdish-led militias, took from the jihadists of the Islamic State. That put about one-quarter of Syria’s territory, which holds valuable agricultural land and oil reserves, under the control of militias backed by the United States and supported by about 2,000 American soldiers.
It also angered Turkey, which sees Syria’s Kurdish fighters as a security threat and has vowed to attack them in the near future. Kurdish control of the region is also opposed by the government of President Bashar al-Assad as well as its Russian and Iranian backers, who want the territory to fall back under the control of Damascus.
For the most part, the other powers in Syria’s multisided war have avoided attacking the area for fear of provoking the United States. But Mr. Trump’s surprise announcement last week that he would pull American troops out of Syria cleared the way for a possible scramble by those competing forces to take advantage of the resulting vacuum.
In a statement issued on Friday, Syria’s most powerful Kurdish militia, the People’s Protection Units, or Y.P.G., called on the Syrian government to send troops to the city of Manbij to ward off a possible attack by Turkey.
The call was notable in that a United States ally, the Kurds, was calling on an enemy of the United States to protect it against another United States ally. The Kurds see Mr. Trump’s decision as a betrayal.
Fearing that the Americans would withdraw, Syria’s Kurdish leadership had been in talks with the Assad government about reconciling.
Kurdish officials said on Friday that a preliminary deal had been reached over the deployment of Syrian troops in Manbij.
Not long after that announcement, the Syrian government said its forces had entered the city and planted the Syrian flag, although residents of the city said that Syrian forces had not yet entered the city but were on the outskirts.