Boris Johnson has branded Vladimir Putin a “dictator” as he suggested the UK will support Ukraine “militarily” to thwart the invasion.
Delivering a No 10 address, the prime minister vowed Russia will never “subdue the national feeling of the Ukrainians and their passionate belief that their country should be free”.
Mr Johnson accused the Russian president of authorising “a tidal wave of violence against a fellow Slavic people” – as he prepares to announce “massive” sanctions.
And, hinting at military support, he said: “Our mission is clear. Diplomatically, politically, economically – and eventually, militarily – this hideous and barbaric venture of Vladimir Putin must end in failure.”
The UK, along with the rest of Nato, has ruled out putting troops on the ground – but several Tory MPs are calling for the UK to help enforce a no-fly zone, or even provide air support to Ukraine.
Mr Johnson said his “worst fears have now come true and all our warnings have proved tragically accurate”, with the overnight invasion.
“Innumerable missiles and bombs have been raining down on an entirely innocent population. A vast invasion is underway by land by sea and by air,” he warned.
“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.”
The prime minister added: “We – and the world – cannot allow that freedom just to be snuffed out. We cannot and will not just look away.”
But, moments later, the prime minister’s spokesman said the UK will not be intervening militarily, beyond strengthening Ukranian forces.
“Our expectation is that the Ukrainian people will fight, will engage with Russian forces. We are providing military, defensive military capability,” he said.
The spokesman also said the issue of a no-fly zone was a matter for Nato – not London – and that he was “not aware” of any such plans.
The UK’s beefed-up sanctions will be unveiled later on Thursday – after the initial package, on Tuesday, was widely criticised as feeble.
They are likely to include banning Russia from the SWIFT international payments system and ending its ability to raise funds on London markets, by issuing sovereign debt.
Experts warn that the measures, while hitting Russia hard, will also rebound on the UK and other countries by hiking already-soaring energy bills even further, as well as supermarket prices.
Delivering a speech, Rishi Sunak said he had spoken with the Bank of England governor, as they monitor the impact of the invasion on the stability of financial markets.
In his statement, Mr Johnson said: “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.”
Some experts have warned Western sanctions will come too late to persuade the Kremlin to change course, amid growing speculation about the Russian’s president’s mental state.
But Mr Johnson said, of Ukraine’s plight: “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 is an attack on democracy and freedom in East Europe and around the world.”