A Department of Defense statement said the US contractor had been killed and the others wounded "after a one-way unmanned aerial vehicle struck a maintenance facility on a Coalition base near Hasakah in northeast Syria."

Another US contractor was also injured in the UAV attack, the Pentagon said.

Defense Secretary Lloyd Austin said he had authorized "precision airstrikes tonight in eastern Syria against facilities used by groups affiliated with Iran's Islamic Revolutionary Guards Corps."

"The airstrikes were conducted in response to today's attack as well as a series of recent attacks against Coalition forces in Syria by groups affiliated with the IRGC," he added.

The US intelligence community "assess the UAV to be of Iranian origin," the Pentagon statement said.

Hundreds of American troops are in Syria as part of a coalition fighting against remnants of the Islamic State (IS) group and have frequently been targeted in attacks by militia groups.

The US troops support the Syrian Democratic Forces (SDF), the Kurds' de facto army in the area, which led the battle that dislodged IS from the last scraps of their Syrian territory in 2019.