Boris Johnson has warned Europe is facing a “very dangerous moment” as he met with Nato chiefs to discuss the crisis in Ukraine.
Britain was sending a “strong” triple warning to Vladimir Putin on Thursday not to invade Ukraine as Russia was starting a huge military exercise with Belarus.
The message was being delivered by MrJohnson in Brussels for top-level talks with Nato , Foreign Secretary Liz Truss in Moscow and Defence Secretary Ben Wallace in London.
The Prime Minister, who was also heading to Warsaw in a show of support to Poland, stressed the West must stand firm in the face of Mr Putin’s “coercive diplomacy”, with the UK having taken a tougher stance than some other European allies including Germany.
He said: “I believe that if we can keep a strong grip on the fundamentals, those fundamental principles that define our alliance and combine strong deterrents with diplomacy then we can find a way through this crisis.
“But the stakes are very high and this is a very dangerous moment and at stake are the rules that protect every nation, big and small.”
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.”
Mr Johnson also emphasised that Nato “must draw lines in the snow” and be “clear there are principles upon which we will not compromise”.
Rejecting the Kremlin’s demand that Ukraine must not be able to join Nato, he added: “That includes the security of every Nato ally and the right of every European democracy to aspire to Nato membership.”
Nato secretary general Jens Stoltenberg also warned this is a “dangerous moment” for European security as the pair held a joint press conference in Brussels.
Ms Truss told Russian Foreign Minister Sergei Lavrov that an invasion of Ukraine would be “disastrous” and urged Russia to abandon “Cold War rhetoric” and avoid war.
Speaking at a joint press conference with Mr Lavrov, Ms Truss accused Russia of "attempting to destabilise Ukrainian democracy".
"These acts have actually had the effect of strengthening Nato's resolve and turning the Ukrainian people further away from Russia," she said.
She warned that a Russian invasion would result in a "prolonged and drawn-out conflict" and the UK would put in place "severe sanctions targeting individuals and institutions".
Mr Lavrov denied that Russia was showing any aggression toward Ukraine and said their were no plans to invade.
He said Russian was “the one being threatened”.
Sir Keir Starmer and shadow defence secretary John Healey are also meeting with Mr Stoltenberg in Brussels this afternoon.
The Labour leader is expected to say he is “proud of the work Nato has done, is doing and will continue to do to protect our freedoms, promote peace and resist aggression, including as we see today in Ukraine”.
Mr Wallace, who is heading to Moscow in coming days, warned Russia that an invasion of Ukraine would be a “lose-lose” situation.
He told Times Radio: “No-one is going to win from an aggressive invasion of a sovereign state.”
He urged Moscow to recognise that the US, Britain and other allies were “serious” about consequences of a military incursion in terms of sanctions and other responses.
However, he also pushed Cold War-style confidence-building moves between Russia and the West to defuse the crisis.
Mr Johnson announced last night that 1,000 British troops are being put on standby in case of a humanitarian crisis in eastern Europe if the current Russian military build-up leads to war.
British officials warned any further Russian incursion into Ukraine would be a “humanitarian disaster” leading to a mass displacement of people, which would particularly affect countries like Poland and Lithuania.
Additional troops are being paced on readiness to provide a humanitarian response if required, although they could also be used to provide further support to allies in the region.
French President Emmanuel Macron, who met Mr Putin in Moscow earlier this week, said the Russian president had told him he was not seeking to escalate the situation.
Their talks raised hopes that a diplomatic solution could be reached to avoid conflict.
However with large-scale Russian military exercises starting in Belarus, which also borders Ukraine, there are fears they could be cover for an attack.
