The US-led coalition said on Tuesday it had shot down an armed "pro-Syrian regime" drone that had been bearing down on its forces near a garrison close to the border with Iraq in Syria's southeast.
In a statement, US forces said the drone was fired on after it "displayed hostile intent and advanced on coalition forces", and a Western intelligence source said the so-called UAV (Unmanned Aerial Vehicle) was Iranian.
The statement said the location was close to where another "pro-regime" drone - which intelligence sources separately identified as Iranian - was shot down on June 8 after dropping bombs near coalition forces.
In Syria's complicated multi-sided conflict, Washington backs a coalition of rebel forces fighting both President Bashar al-Assad and Islamist militants, while Assad is backed by Russia, Iran and Shi'ite militia.
In an indirect reference to Iranian-backed forces that have been gathering in the eastern desert region, the coalition statement cited a recent escalation of tensions and said it would not "tolerate any hostile intent and action of pro-regime forces".
The US military has repeatedly warned forces fighting on Assad's side to stay away from a "deconfliction zone", agreed with Russia, near a garrison used by US Special Forces and US-backed militia around Al Tanf.