US shoots down 'hostile' drone on Syria-Iraq border

The US-led coalition has shot down an armed "pro-Syrian regime" drone that it says was bearing down on its forces near a garrison close to the border with Iraq in Syria's southeast.

In a statement on Tuesday, 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.

Al-Tanaf, on the key highway connecting Damascus with Baghdad, has been menaced by a surge of Iran-backed troops loyal to Syrian President Bashar al-Assad.

Coalition forces use the area -- just northeast of the Jordanian border -- as a training and staging area for attacks against IS.

The incident has similar hallmarks to a June 8 shoot-down, when a US F-15 destroyed a pro-regime drone after it dropped what turned out to be a dud bomb near US-backed local forces.

It also comes after an American F/A-18E Super Hornet fighter jet shot down a Syrian SU-22 fighter-bomber Sunday in northern Syria as it "dropped bombs" near the Syrian Democratic Forces, a US-backed alliance fighting IS.

"Hostile intent and actions of pro-regime forces toward coalition and partner forces in Syria conducting legitimate counter-ISIS operations will not be tolerated," the coalition statement read.

The downing of the regime jet led Moscow to say it would sever a vital hotline it uses to communicate with the US coalition to avoid mishaps in Syria's increasingly crowded and complicated battlespace.