The US-led coalition fighting Islamic State has said it hit pro-Syrian government forces near the border with Jordan that "posed a threat" to US 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 those troops from moving into the "de-conflicted area", a coalition statement said.

The de-conflicted zone, agreed between the US and Russia, is located around Tanf, where the borders of Jordan, Syria and Iraq meet.

The statement said coalition forces have been operating in the area "for many months training and advising vetted partner forces" in the battle against IS.

Syrian activists said the strike destroyed vehicles and left casualties.