Russia has warned the US-led coalition fighting in Syria that it will view its aircraft as targets, after a Syrian military plane was shot down.
The coalition said it had shot down the Syrian Su-22 after it bombed US-backed fighters in Raqqa province on Sunday.
Russia, Syria's main ally, said it was also halting communications with the US aimed at preventing air incidents.
Syria condemned America's "flagrant attack", saying it would have "dangerous repercussions".
The incident comes at a time when the US-led coalition and the fighters its supporting on the ground are battling to oust so-called Islamic State (IS) from its Syrian stronghold of Raqqa.