US army issues warning to Iran-backed Syria militia

The US military estimates that a large number of Iran-backed fighters have remained within a "deconfliction" zone meant to ensure the safety of US-led coalition forces, and views them as a threat.

"We have increased our presence and our footprint and prepared for any threat that is presented by the pro-regime forces," said the spokesman, US Army Colonel Ryan Dillon, referring to Iran-backed forces supporting Syrian regime president Bashar al-Assad.

A large number of the fighters have also amassed directly outside the coalition training facility At Tanf, located in southeast Syria near the Iraqi border.

"We see that as a threat," Dillon said.

A copy of the leaflets provided to Reuters by the Pentagon told the Iran-backed fighters that any movement towards the At Tanf garrison "will be seen as hostile intent and we will defend our forces."

"You are within an established deconfliction zone, leave the area immediately," another read.

US-backed Syrian rebels recaptured At Tanf from Islamic State fighters last year, and regional intelligence sources say they intend to use it as a base to capture the border town of Bukamal, an important supply route for IS.

Badia, the south-eastern area of the Syrian desert, has become a critical front in fighting between Assad forces, backed by Iranian militias, and opposition rebels.

Both side are competing to recapture territory held by the Islamic State as it comes under heavy attack in Iraq and Syria.