Syrian government forces have entered the centre of the once Kurdish-held northern town of Manbij, about 30 kilometres south of the Turkish border, and raised the national flag, Syrian state media say.
A video released by SANA showed some people gathered in the main square waving Syrian flags Tuesday morning.
Syrian President Bashar al-Assad's forces had left the area at the height of the civil war, leaving it to the Kurdish groups.
The flashpoint area housed U.S. troops who patrolled the region since 2017 to deter a confrontation between Turkey and Kurdish fighters.
The Kurdish Hawar News Agency said American troops left the town on Tuesday morning moving southeast about 35 kilometres toward the Tishrin Dam on the Euphrates river.
On Monday, Turkish President Recep Tayyip Erdogan said his military was ready to begin moving into the city.
One Turkish soldier was killed and eight others were wounded on Tuesday after Kurdish fighters defended their position in Manbij, Turkey's Defence Ministry said. At least 15 fighters had been "neutralized" in retaliation, the ministry said.
Near a different border town in northeast Syria, Ras al Ayn, Turkish artillery were pounding suspected Kurdish positions as Turkey's military incursion entered its seventh day.
An Associated Press journalist reported heavy bombardment of targets in the countryside of Ras al Ayn, days after Turkey announced it had captured the town. Turkish jets also carried out at least one airstrike.
The Syrian Observatory for Human Rights, a war monitor, reported Kurdish fighters had retaken the town.
Erdogan defended Turkey's offensive in an op-ed in the Wall Street Journal, calling on the international community to support the initiative or "begin admitting refugees" from Syria.
Humanitarian crisis looms
The Kurdish-led administration in northern Syria says humanitarian conditions are getting worse by the day since Turkey began its invasion last week.
Tuesday's statement warned humanitarian assistance is much needed after international organizations stopped their activities and withdrew their employees.
The region's semi-autonomous administration said there is a lack of medical equipment and medicines after "most of the medical centres stopped functioning."
The administration called on the United Nations, the Arab League and the European Union to "intervene quickly and provide medical, logistical and humanitarian assistance to the displaced to avoid the humanitarian crisis."
The U.S.-based Mercy Corps said nearly 130,000 have been forced to flee the region.
"This is our nightmare scenario," said Made Ferguson, the aid organization's deputy country director for Syria.
"There are tens of thousands of people on the run and we have no way of getting to them. We've had to pull our international staff out of northeast Syria," Ferguson said. "We just cannot effectively operate with the heavy shelling, roads closing, and the various and constantly changing armed actors in the areas where we are working."
Kurdish mayors detained
Turkish police detained four mayors from a pro-Kurdish party in dawn raids, widening a crackdown since Ankara launched its incursion into northern Syria, state media and the party said on Tuesday.
The pro-Kurdish People's Democratic Party (HDP) mayors of the Kurdish-majority Hakkari, Yuksekova, Ercis and Nusaybin, districts near Turkey's borders with Syria and Iraq, were detained over terrorism links, the HDP and Anadolu news agency said, without elaborating.
Erdogan and his government accuse the HDP of being linked to the Kurdistan Workers Party (PKK) militant group, and thousands of its members have been prosecuted for the same reason, including its leaders. The HDP denies such links.
While most of Turkey's opposition parties have backed the operation, the HDP has called for it to stop, describing it as an "invasion attempt." HDP said the operation was an attempt by the government to drum up support amid declining public backing.
The HDP said 151 of its members, including district officials, had been detained over the past week since Turkey and its Syrian rebel allies launched the assault.
Last week, Turkish police launched criminal investigations into the HDP's co-chairs over their criticism of the military operation and started probes into more than 500 social accounts over "terrorist propaganda" criticizing the offensive.
Authorities launched similar investigations after each of Turkey's two previous cross-border operations into Syria. More than 300 people were detained for social media posts criticizing Turkey's offensive into northern Syria in January 2018.