An attack was launched on Friday night against a position belonging to US-backed, Kurdish-led forces in eastern Syria's Deir Az-Zour province.
The attack against the Syrian Democratic Forces (SDF) was believed to have been carried out by gunmen affiliated with Arab tribes.
Activist Wissam Al-Akidi told The New Arab's Arabic sister service Al-Araby Al-Jadeed that there was an attack on an SDF military checkpoint on the outskirts of the town of Al-Tayyana. The extent of the losses was not clear.
A group of young people belonging to Arab tribes have been carrying out surprise attacks against the SDF for around 10 days following the Kurdish-led organisation's recapture of territory in Deir Az-Zour province.
There had been fierce clashes between the group and Arab fighters, including from the formerly SDF-affiliated Deir Az-Zour Military Council militia.
Meanwhile, the SDF arrested eight people, including civilians, during a raid-and-arrest campaign in the town of As-Susa in the province.
One of the group's reconnaissance aircraft also flew through the area.