US shoots down Syria warplane that 'hit allies' close to Raqqa

This further complicates country's six-year war, escalating tensions between US and regime forces

An American fighter jet has for the first time downed a Syrian warplane that Washington accused of attacking US-backed fighters, in a new escalation between the United States and regime forces.

The incident further complicates the country's six-year war and comes as a US-led coalition and allied fighters battle to oust the Islamic State group from its Syrian bastion Raqa.

Iran on Sunday launched missiles from its territory against alleged IS positions in eastern Syria for the first time, in response to an IS-claimed attack in Tehran.

Analysts say neither Washington nor President Bashar al- Assad's regime appear to be seeking further confrontation but warn that the risks are high in Syria's increasingly crowded battlefields.

The Syrian jet was shot down yesterday evening after regime forces engaged fighters from the Syrian Democratic Forces (SDF), an alliance battling with US support against IS, in an area close to Raqa.

The American F/A-18E Super Hornet shot down the Syrian SU-22 around 7 pm as it "dropped bombs near SDF fighters" south of the town of Tabqa, the coalition said in a statement.

It said that several hours earlier, regime forces had attacked the SDF in another town near Tabqa, wounding several and driving the SDF from the town.

The coalition said the Syrian warplane had been shot down "in accordance with rules of engagement and in collective self-defence of Coalition partnered forces".

Syria's army disputed the account, saying its plane was hit while "conducting a mission against the terrorist Islamic State group."

It warned of "the grave consequences of this flagrant aggression".

Regime ally Moscow also condemned the downing of the Syrian plane, with deputy foreign minister Sergei Ryabkov saying: "This strike has to be seen as a continuation of America's line to disregard the norms of international law... What is this if not an act of aggression?"

The incident was the latest skirmish between the US-led coalition and regime forces in the increasingly tense and crowded space in Syria's north and east.

The coalition has for months backed SDF forces in their bid to capture Raqa, an operation in which the regime has not been involved.

The SDF entered Raqa for the first time earlier this month and now holds four neighbourhoods in the east and west of the city.

Damascus has instead turned its focus further east, to the largely IS-held oil-rich province of Deir Ezzor, where government forces are besieged in part of the provincial capital. It is advancing towards the region on three fronts, south of Raqa, through the Badia desert region in central Syria, and along Syria's eastern border.