Europe is facing its biggest security crisis in decades, British Prime Minister Boris Johnson said, noting that Ukraine could be offered further support if Russia invades, AP reported.

The prime minister said he did not rule out additional military assistance to Ukraine, warning that a Russian invasion would lead to "serious bloodshed".

Speaking alongside NATO Secretary-General Jens Stoltenberg at the alliance's headquarters in Brussels, Johnson urged Russia to engage in meaningful negotiations because it is “far better to begin a discussion now than to have a catastrophe”.

The UK has already provided Ukraine with some 2,000 anti-tank missiles, and Johnson has said that he may go even further.

“The Ukrainians are well prepared, there are things we’ve offered that they, in fact, don’t seem to need because they think they have them in enough numbers already... “But I want to stress it would be an absolute disaster if it was to come to that and if there was to be serious bloodshed on Ukrainian soil.”

He said the intelligence on the prospect of an invasion was “grim” but he did not believe Vladimir Putin had yet decided on whether to act.

“I honestly don’t think a decision has yet been taken but that doesn’t mean that it’s impossible that something absolutely disastrous could happen very soon indeed,” he added.

“Our intelligence, I’m afraid to say, remains grim. We’re seeing the massing of huge numbers of tactical battalion groups on the border with Ukraine. This is probably the most dangerous moment in the course of the next few days in what is the biggest security crisis Europe has faced for decades,” the British Prime Minister said.