The US-led coalition fighting the Islamic State (IS) group says it has shot down an armed pro-Syrian regime drone that had been bearing down on its forces in Syria's south-east.
- US says drone "displayed hostile intent"
- Incident happened in area close to where US shot another drone down earlier this month
- US recently brought down Syrian military jet
It marked the second time in three days US forces have shot down an aircraft operated by Damascus or its allies in Syria, and reflected mounting tensions over a stretch of the Syrian-Iraqi frontier where US forces have established a base.
The US military said the drone was Iranian-made but it was unclear who was operating it.
US forces said the drone was fired on after it "displayed hostile intent and advanced on coalition forces", US forces said in a statement.
The area falls in a part of Syria that was recently identified as a military priority by Damascus, and is seen as strategically important for Iran as it seeks to secure a land corridor between forces it backs in Syria and Iraq.
The coalition statement said the location was close to where another "pro-regime" drone — which intelligence sources had also identified as Iranian — was shot down on June 8 after dropping bombs near coalition forces.
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".
Tensions escalated on Sunday as the US Army brought down the jet near Raqqa and Iran launched missiles at IS targets in eastern Syria — the first time each state has carried out such actions in the multi-sided Syrian war.
Russia, like Iran an ally of President Bashar al-Assad, issued a warning of its own to the United States in response to the downing of the Syrian jet, saying on Monday it would view as targets any planes flying west of the Euphrates River, though it stopped short of saying it would shoot any down.
Australia said it would temporarily halt air operations over Syria after the plane was downed.
In Syria's tangled conflict, Washington backs a coalition of rebel forces fighting both Mr Assad and Islamist militants, while Mr Assad is backed by Russia, Iran and Shiite militia.
The US military has repeatedly warned forces fighting on Mr 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.
On several occasions in recent weeks, warplanes of the US-led coalition have also struck pro-government forces to prevent them advancing from the Al Tanf garrison in south-eastern Syria at a spot where the country's borders join Iraq and Jordan.
Washington also described those strikes as self-defence.
The competition between the Syrian army and the militias and US-backed Free Syrian Army rebels has stepped up in the Badia desert that stretches to the Iraqi border after IS abandoned large swathes of territory as it defends Raqqa and Deir Zor.
The Syrian army has been able to make rapid advances allowing them to reach the border for the first time in years.