Russia has warned it will treat American and British jets operating in parts of Syria where its air forces are present as “targets”, after the US shot down a Syrian warplane for the first time in the six-year-war.

Moscow, Syria's main ally, announced that it would start tracking jets and drones of the US-led coalition and halt an incident-prevention hotline with America, which was set up to avoid accidents in the crowded skies above Syria.

"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," the defence ministry warned.

On Monday Sean Spicer, Donald Trump's spokesman, insisted the US would not back down and would "do what we can to protect our interests."

Mr Spicer added: "The escalation of hostilities among the many factions that are operating in this region doesn't help anybody. And the Syrian regime and others in the regime need to understand that we will retain the right of self-defence, of coalition forces aligned against ISIL"

The Syrian SU-22 fighter bomber was shot down by an American F18 Super Hornet on Sunday after it had dropped bombs near the US-backed Syrian Democratic Forces (SDF) north of the Islamic State of Iraq and the Levant (Isil)-held city of Raqqa.