The Syrian army's deployment near the Turkish border came hours after Syrian Kurdish forces previously allied with the U.S. said they had reached a deal with President Bashar Assad's government to help fend off Turkey's invasion, now in its sixth day.
The announcement of a deal between Syria's Kurds and its government is a major shift in alliances that came after President Donald Trump ordered all U.S. troops withdrawn from the northern border area amid the rapidly spreading chaos.
The shift sets up a potential clash between Turkey and Syria and raises the specter of a resurgent Islamic State group as the U.S. relinquishes any remaining influence in northern Syria to Assad and his chief backer, Russia.
The fighting also seems likely to endanger, if not altogether crush, the brief experiment in self-rule set up by Syria's Kurds since the war began. "We are going back to our normal positions that are at the border," said a Syrian officer said, as embattled Kurdish authorities invited the government to retake towns and villages in the north.
Syrian troops arrived on Monday in the northern province of Raqqa aboard buses and pickup trucks with mounted heavy machineguns. Turkey has pressed on with its invasion of northern Syria, warning its NATO allies in Europe and the United States not to stand in its way.
Turkish troops and Syrian proxy forces have steadily pushed their way south of the border, clashing with the Kurdish fighters over a stretch of 200 kilometers (125 miles). The offensive has displaced at least 130,000 people.
Turkey's president signaled that it was ready to launch an assault on the city of Manbij, where Kurdish-led groups invited Syrian government forces to re-enter and defend the town. "We are about to implement our decision on Manbij," President Recep Tayyip Erdogan told reporters on Monday.
He added that Turkey's aim would be to return the city to Arab populations whom he said where its rightful owners. Turkish forces were already positioned at the city's edge, according to CNN-Turk. Erdogan has already said Turkey will not negotiate with the Syrian Kurdish fighters, which it considers "terrorists" for links to a long-running Kurdish insurgency within its own borders.
Syrian state media reported late Sunday that government troops were marching toward Manbij — as well as the border town of Kobani that in 2015 witnessed the Islamic State group's first defeat in a battle by U.S.-backed Kurdish fighters.
In another direction, Syrian troops moved east from Aleppo province to Raqqa where state media said they had reached Ein Issa. Heavy fighting the previous day there reached a Kurdish-run displaced-person camp that is home to some 12,000 people, including around 1,000 wives and widows of IS fighters and their children. Hundreds are believed to escaped amid the chaos.
The Syrian army also moved into the town of Tal Tamr, which is about 20 kilometers (12 miles) from the Turkish border, and Tabqa, known for its dam on the Euphrates River and its nearby air base that carries the same name.
SANA said government forces planned to "confront the Turkish aggression," without giving further details. Photos posted by SANA showed several vehicles and a small number of troops in Tal Tamr. Tal Tamr is a predominantly Assyrian Christian town that was once held by IS before it was retaken by Kurdish-led forces. Many Syrian Christians, who make up about 10 percent of Syria's pre-war population of 23 million, left for Europe over the past 20 years, with the flight gathering speed since the country's conflict began in March 2011.
Mroue reported from Beirut. Associated Press writers Albert Aji in Damascus, Syria and Suzan Fraser in Ankara, Turkey, contributed to this report.