Russia could face a retaliatory chemical weapons attack if it uses lethal gases on innocent civilians in Ukraine, according to Joe Biden.

The US President issued the warning as world leaders gathered to discuss counter-measures against Vladimir Putin, who is suspected of using the barbaric munitions.

Boris Johnson warned the Kremlin dictator that he would face “catastrophic consequences” if he did so, as concerned Western leaders increased preparations to ship hazmat suits to war-torn Ukraine.

In the event of a chemical attack, the PM did not rule out putting boots on the ground, as Mr Biden warned that the West could launch a “response in kind” at the historic summit at Nato’s headquarters.

It came as Nato increased its chemical and nuclear defences and announced the deployment of 6,000 soldiers in four new battalions to Eastern Europe to supplement the 40,000 already fighting Putin’s forces.