Prime Minister Boris Johnson vowed the UK and its allies would respond to Russia's invasion of Ukraine and said 'this hideous and barbaric venture of Vladimir Putin must end in failure'.
In a TV address to the nation, Mr Johnson promised a 'massive' package of sanctions' 'designed to hobble the Russian economy' and said the world could not allow the freedom of Ukraine to be 'snuffed out'.
"We cannot and will not just look away," said the prime minister.
He spoke after Russian forces have launched a major military assault on Ukraine, with reports of missile strikes and explosions near major cities.
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Mr Johnson said: "A vast invasion is under way by land, by sea and by air. And this is not, in the infamous phrase, some faraway country of which we know little.
“We have Ukrainian friends in this country, neighbours, co-workers. Ukraine is a country that for decades has enjoyed freedom and democracy, and the right to choose its own destiny.
“We and the world cannot allow that freedom just to be snuffed out. We cannot and will not just look away.”
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He went on that the Putin regime would be condemned to 'pariah status' after unleashing a 'tidal wave of violence' against Ukraine.
The Prime Minister said the UK stood with Ukraine in its 'moment of agony'.
"I say to the Ukrainians in this moment of agony, we are with you. We are praying for you and your families, and we are on your side,” he said.
"If the months ahead are grim and the flame of freedom burns low, I know that it will blaze bright again in Ukraine.
"For all his bombs and tanks and missiles, I don’t believe the Russian dictator will ever subdue the national feeling of the Ukrainians and their passionate belief that their country should be free."
He added: "It’s because we’ve been so alarmed in recent months at Russian intimidation that the UK became one of the first countries in Europe to send defensive weaponry to help the Ukrainians.
"Other allies have now done the same and we will do what more we can in the days ahead.
"Today, in concert with our allies we will agree a massive package of economic sanctions designed in time to hobble the Russian economy.
"And to that end, we must also collectively cease the dependence on Russian oil and gas that for too long has given Putin his grip on Western politics.
"Our mission is clear. Diplomatically, politically, economically, and eventually, militarily, this hideous and barbaric venture of Vladimir Putin must end in failure."
Mr Johnson concluded by saying: "I say to the British people, and all who have heard the threats from Putin against those who stand with Ukraine, we will, of course, do everything to keep our country safe."
He added: "We will work with them, for however long it takes, to ensure that the sovereignty and independence of Ukraine is restored.
"Because this act of wanton and reckless aggression is an attack not just on Ukraine, it’s an attack on democracy and freedom in eastern Europe, and around the world.
"This crisis is about the right of a free, sovereign, independent European people to choose their own future.
"That is a right that the UK will always defend."
