Russia on Monday said it would track as "targets" any US-led coalition planes operating west of the Euphrates river in Syria, and condemned the shooting down of a Syrian government plane by US forces.
The US shot down a Syrian air force Su-22 over Tabqa - 55km west of Raqqa city - on Sunday, saying the plane was threatening allies from the Syrian Democratic Forces as they fought intense ground battles with Syrian government allies around Raqqa.
Russia's deputy defence minister, Sergei Ryabkov, said the incident was an "act of aggression". His ministry said the act voided a cooperation deal and that a military hotline for avoiding incidents in Syrian airspace had been suspended.
"The command of the coalition forces did not use the established communication channel for preventing incidents in Syrian airspace," the defence ministry said in a statement.
As a result, it now "ends cooperation with the American side from 19 June based on a memorandum for prevention of incidents and ensuring safety of air flights during operations in Syria, and demands a careful investigation by the US command" of the downing.
"Any flying objects, including planes and drones of the international coalition, discovered west of the Euphrates river will be tracked as aerial targets by Russia's air defences on and above ground," it said.
The US military said later on Monday that it was repositioning its aircraft to ensure aircrew safety.