A pro-Syrian government drone has been shot down by the US after firing at coalition forces, according to the country's military.
It's the first time pro-Syrian government units have attacked US-led coalition forces, said a spokesman.
No coalition forces are reported to have been hurt in the incident, which happened between Syria and Iraq. US Colonel Ryan Dillon said:
"[Even if the drone had only been firing a warning] it was something that showed a hostile intent, a hostile action and posed a threat to our forces because this drone had munitions that were still on it".
It is not yet known which of the Syrian pro-government groups was flying the drone.
It comes after the US-led coalition fighting the so-called Islamic State said it hit pro-Syrian government forces near the border with Jordan that "posed a threat" to American forces and rebel groups in the area.
The coalition hit the pro-Syrian government forces after warning shots, a show of force and apparent Russian attempts failed to dissuade them from moving into the "de-conflicted area", a coalition statement said.
Speaking to reporters, US Defence Secretary Jim Mattis said the US will defend its troops in case of "aggressive" steps against them. He said:
"We are not increasing our role in the Syrian civil war, but we will defend our troops."
"And that is a coalition element made up of more than just US troops, and so we will defend ourselves [if] people take aggressive steps against us."