The strike, confirmed by state news agency SANA, was carried out after the regime checkpoint refused passage to the patrol in the northeastern city, the Syrian Observatory for Human Rights said.

"One soldier was martyred and two others wounded... when a US aircraft targeted an army checkpoint," SANA reported, giving a lower death toll.

It said the strike came "southeast of Qamishli after the checkpoint prevented a US occupation convoy from passing".

Monday's strike was the first deadly incident of its kind in six months, the Observatory said, although tensions are not unusual in the area, where the web of security responsibilities is complex.

Kurdish and US coalition forces, as well Russian and government troops, are all deployed in the area.

There was no immediate comment from the US-led coalition, which is allied with the Kurdish-dominated Syrian Democratic Forces in the northeastern region.