Russia has warned the US-led coalition in Syria that its aircraft will be regarded as targets after the US shot down a Syrian military aircraft on June 18.

“Any aircraft, including the international coalition’s planes and drones, discovered west of the river Euphrates, will be accompanied by ground and air-based anti-aircraft defences as aerial targets,” the defence ministry in Moscow said in a statement the following day, and suspended a de-confliction agreement aimed at preventing incidents between US and Russian aircraft.

The coalition said the Syrian Su-22 fighter-bomber had dropped bombs near US-backed fighters battling forces of Islamic State in Raqqa, the jihadi group’s proclaimed capital. While the White House said it retains the right to self-defence in Syria, Russia’s foreign ministry reacted strongly to the incident.

“What is this other than an act of aggression in violation of the norms of international law?” Russian Deputy Foreign Minister Sergei Ryabkov said. “This, if you like, is help for the terrorists that the US are fighting under what they call their anti-terrorism policy.”

However, the Russian statements stopped short of openly saying coalition aircraft would be shot down. Reuters also quoted a US military spokesman as saying the coalition was now repositioning aircraft over Syria to ensure the safety of US crew members.

The chairman of the US Joint Chiefs of Staff, General Joseph Dunford, said efforts were underway to re-establish the “deconfliction” communications line with Russia, and that it had remained in use “over the last few hours”.

These communications were also suspended between the two sides in April after the US launched cruise missiles at a Syrian government airbase in response to a suspected chemical weapons attack on a rebel-controlled town in Syria's Idlib province. The US and Russia agreed to resume communications in May.