Russia has pledged to start treating American planes like ‘targets’ in large areas of Syria.
The Middle Eastern civil war has now raged for seven years and threatens to destabilise the entire region.
Putin’s new escalation comes after the US downed a Syrian government jet.
America is supporting insurgents who are battling Basher al-Assad’s Baathist regime while also fighting so-called Islamic State in different areas.
However, Russia is backing the dictator.
The US took out the government fighter jet because it had dropped bombs close to American allies.
The Russian defence ministry will now target all US-led coalition planes if they cross west of the Euphrates River.
Neighbours such as Jordan have joined with America and Gulf allies Saudi Arabia, the UAE and Qatar.
However they will now be under threat from the Russian airforce.
Kremlin officials have now demanded that the Americans provide a full explanation for shooting the Syrian government SU-22.
Theresa May spoke out on the development, saying: ‘There are deconfliction arrangements in place already in relation to activity that takes place over the skies of Syria and those deconfliction arrangements will continue.’
It was added later that the UK government wanted Russia to use measures that ‘reduce the chance of misunderstandings over what is a crowded airspace’.