The Syrian army said it entered Manbij on Friday for the first time in years, after the Kurdish YPG militia urged Damascus to protect the town from the threat of Turkish attacks.
It was unclear whether the government forces had spread out in the town, where US forces operate and have a military base.
With the YPG at its forefront, Syrian Democratic Forces (SDF) seized Manbij in 2016 from Islamic State, a milestone in the US-backed battle against the jihadists.
The Manbij Military Council, fighters allied to the SDF, hold the town in northern Syria, which lies on a front with Turkey-backed rebels. Ankara deems the Kurdish YPG fighters a threat and has vowed to crush them.
The Syrian army said in its statement on Friday that its troops had raised the national flag in Manbij and would guarantee security “for all Syrian citizens and others present in the area”.
The Syrian Observatory for Human Rights, a Britain-based war monitor, said the troops had deployed only along the edges of Manbij, standing between the town and Turkey‘s rebel allies.
President Donald Trump’s abrupt decision to pull out some 2,000 US troops, whose presence has deterred Turkey, has alarmed the SDF, which controls much of northern and eastern Syria.
The YPG says its fighters previously withdrew from Manbij to fight Islamic State jihadists in eastern Syria.
“So we invite the Syrian government which we belong to…to send its armed forces to take over these positions and protect Manbij in the face of Turkish threats,” it said on Friday.