Defence Secretary Ben Wallace has warned Russian President Vladimir Putin to not 'underestimate the West' - noting that if allies stuck together, Russia's invasion would fail.
In an interview with The Sunday Telegraph, Mr Wallace called on the West and said they 'must not be afraid of Putin'.
He claimed Putin was 'acting irrationally and inflicting horrors on Ukraine' by continuing his invasion.
He said: "The thing to say to Putin is don't underestimate us, don't test us.
"History is littered with authoritarian leaders underestimating the wider West and the United Kingdom. He clearly underestimated the international community.”
He added: “If we stick together and refuse to be intimidated then I believe he will fail.”
It comes after Russia stepped up its warning to Western nations intervening in the war, comparing economic sanctions akin to a declaration of war.
Mr Putin warned on Saturday that declaring a no-fly zone over Ukrain would be considered as participation in the conflict.
He added that Russia would view 'any move in this direction' as an intervention that 'will pose a threat to our service members'.
“That very second, we will view them as participants of the military conflict, and it would not matter what members they are,” he said.
But, Ukraine continues to insist that implementing a no-fly zone is the only way to prevent more deaths in the conflict.
Meanwhile, NATO allies have ruled out enforcing a no-fly zone over Ukraine due to fears it could lead to an all-out war with nuclear-armed Russia.
Foreign Secretary Liz Truss, in an interview with the Sunday Express, said the Ukrainian conflict was the 'struggle of our generation'.
She said: “We will continue to support them (the Ukrainians) through thick and thin. We are there for the long haul. This is the struggle of our generation.
"What we are seeing taking place on the streets of Europe is something we have never experienced before in my lifetime. It is the fight for freedom and democracy, and sovereignty and self-determination.”
Earlier today, Prime Minister Boris Johnson praised the British public's response to Ukraine and echoed that Putin would fail.
He said it was "absolutely vital that Vladimir Putin understands that this hideous, barbarous assault cannot succeed and that he will fail".
In a video message on Twitter, Mr Johnson said: “I want to thank businesses, community groups, individuals, sports clubs, who’ve been coming together to support Ukraine.
I think of the group in Northern Ireland that’s got a local warehouse as a centre for supplies to go to the war zone, I think of Inna Schorr, a London-based Ukrainian who’s raising thousands of pounds, while her own family are still back in Ukraine.
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“And don’t forget to for all Ukrainian families here in in the UK, we have ways that you can bring your wider relatives back to the UK.”
Volodymyr Shevetovskyy, 31, and his girlfriend Nadiia Soshenko, 27, from Kyiv, said they were grateful for support from western countries but called for a no-fly zone to be imposed over Ukraine.
Ms Soshenko told the PA news agency: “There are already a lot of deaths in our country.
“Nato is afraid to close the skies saying that they’re afraid to start the third world war. Excuse me, what’s happening right now? Why the whole world can’t stop one insane, mad person? I just honestly do not understand why our people are dying, are dying for what?”
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