"Coalition forces, conducting a patrol near Qamishli, Syria, encountered a checkpoint occupied by pro-Syrian regime forces," coalition spokesman Myles Caggins said.

"The patrol came under small arms fire from unknown individuals. In self-defence, coalition troops returned fire."

Caggins said the patrol returned safely to base after the situation "de-escalated".

An AFP correspondent saw a US flag flying above an armoured vehicle as it left the village.

According to the Syrian Observatory for Human Rights war monitor, loyalists residing in the village of Khirbet Amo tried to block the passage of a US military patrol, firing in the air.

This prompted a response from US troops, who killed a regime loyalist in the clash, the Observatory said.

The coalition did not report such a casuality.

The Russian defence ministry said later that "a conflict took place between US troops and the local population" leaving one resident dead -- identified in the statement as 14-year-old Faysal Khalid Muhammad -- and another wounded.

In a statement, it added that the arrival of Russian troops at the scene had made it "possible to prevent further escalation of the conflict".

Khirbet Amo is among the few areas in the largely Kurdish-held northeast controlled by pro-government forces.

US troops in the region operate as part of the US-led coalition fighting the remnants of IS.

They routinely carry out patrols in the area alongside their Kurdish allies.