United States-backed Kurdish-led fighters in northern Syria on Wednesday fought a deadly battle with Turkish-supported forces who said they intervened after clashes killed dozens in an Arab-majority province further east.
Days of fighting in eastern Syria's Deir Ezzor province, which left 90 people dead, had raised fears of broader conflict in a region where jihadists and foreign powers are present.
The new fighting involving Turkish-backed fighters came hours after the US-backed Syrian Democratic Forces (SDF) declared the "end of military operations" in Syria's east.
Fighting began in Deir Ezzor after the SDF detained Ahmad al-Khabil, head of the Deir Ezzor Military Council.
The SDF had accused him of communicating with the Syrian government, and of alleged drug trafficking and mismanagement leading to an uptick in Islamic State group activities.
The SDF spearheaded the offensive that defeated the IS group's self-declared caliphate in Syria in 2019.
Angry fighters loyal to Khabil launched attacks on the SDF that spiralled into clashes in several villages and towns, according to the Syrian Observatory for Human Rights, a war monitor.
Over the past three days, pro-Turkish Syrian factions intensified their bombardments in support of the Arab fighters clashing with SDF in Deir Ezzor, which is more than 200 kilometres (125 miles) to the east.
Turkish troops and their Syrian proxies hold parts of Syria's northern border.
An AFP correspondent near the SDF-controlled Manbij area in northwest Syria reported dozens of shells fired towards SDF areas.
"Eight Turkish-backed fighters were killed and 13 others were wounded in the clashes," which forced dozens to flee their homes, Observatory director Rami Abdel Rahman told AFP.
The British-based monitor relies on a network of sources on the ground in Syria.
A villager living close to the front line of the latest clashes also said "most residents have left our village".
Faction members "tried to infiltrate villages in the eastern countryside of Manbij, but the SDF blocked them," Abdel Rahman said.
Of the 90 people killed during the Deir Ezzor clashes, most were fighters but the toll included nine civilians, the Observatory said.
Turkish-backed fighters in northern Syria who said they were from Arab tribes had on Monday attacked SDF positions in support of the fighters in Deir Ezzor.
The US embassy to Syria, based outside the country, on Sunday said senior US officials had met with the SDF and community leaders in northeastern Syria.
They agreed on the need for de-escalation and "the dangers of outsiders interfering", the embassy said.
Aron Lund of the Century International think-tank described the area as a "tinderbox".