Beirut - A US warplane shot down an Iranian-made drone operated by pro-regime forces in southern Syria early Tuesday, officials said, in the latest incident in rising tensions between the two sides.

It comes days after a US warplane shot down a Syrian government fighter jet in the north of the country, prompting a furious reaction from Russia.

Moscow has now suspended an incident hotline intended to prevent confrontations in Syria’s crowded air space, and warned it could consider US-led coalition planes “targets”. The rising tensions prompted Australia to announce it was suspending its participation in air missions over Syria as part of the US-led coalition fighting the Islamic State group. In Tuesday’s incident, the US-led coalition said an F-15E Strike Eagle jet destroyed an armed Shahed-129 drone in the early hours of the morning as it neared the Al-Tanaf base along Syria’s eastern border.

“It displayed hostile intent and advanced on Coalition forces,” the statement said.

A US military official told AFP the drone was “on a run toward our folks to drop a munition on them” and was shot down in self-defence. Coalition forces are using the Al-Tanaf base by Syria’s borders with Jordan and Iraq to train anti-jihadist Syrian fighters and stage attacks against IS. But their presence there has led to a series of confrontations with pro-regime forces, including on June 8 when a US plane also downed a drone after it dropped munitions near Al-Tanaf.

That incident followed two others involving US fire against pro-regime forces on the ground as they came close to the garrison.

Tensions have also flared between US forces and the Syrian regime further north, where the coalition is supporting an alliance of Kurdish and Arab fighters battling to oust IS from the city of Raqa.

On Sunday, a US fighter jet downed a Syrian government warplane for the first time in the country’s conflict south of Raqa, sparking an angry reaction from regime ally Russia.

Moscow said it was suspending an incident hotline set up two years ago and warned that it would consider international aircraft operating in central Syria “aerial targets.”

Washington said it would “work diplomatically and militarily... to reestablish deconfliction” but Moscow continued to take a hard line Tuesday even before the latest incident.

“It is absolutely illegal,” Russia’s Deputy Foreign Minister Mikhail Bogdanov said Tuesday of the presence of American forces in Syria.

“There has been neither a Security Council decision, nor a request from the official authorities of the Syrian Arab Republic as a sovereign state,” Russia’s Interfax news reported.

The growing tensions come as the coalition supports the Kurdish-Arab Syrian Democratic Forces (SDF) fighting to take Raqa from IS.