Watch Boris Johnson's interview in full
Boris Johnson has told ITV News Vladimir Putin has "gone into a cul-de-sac" following his invasion of Ukraine and fears the Russian president may try to "double down" in a bid to "Grozny-fy" Kyiv.
The prime minister said Putin will feel it is "very difficult for him to back out" after launching the attack, with reports from Ukraine suggesting the invasion is not going according to plan because of Ukrainian resistance.
Mr Johnson, speaking to ITV News during a visit to Poland, said there's "always an exit route" for Putin to reverse his invasion - "there's got to be a way by which he can deescalate but it's down to him", he said.
ITV News International Affairs Editor Rageh Omaar, who is travelling with the prime minister, reports on Boris Johnson coming face-to-face with Ukrainian frustration at what its people feel is a lack of Western action.
But, the prime minister added, "if you're sitting where he is, his only instinct is going to be to double down and to try and 'Grozny-fy' Kyiv if you know what I mean. And to reduce it to [rubble]."
"I hope he has the wisdom to see that there must be a better way forward but what he's got to do is to disengage, with the column of tanks, 40km long going towards Kyiv, he needs to put those tanks into reverse or turn them round and that is the number one thing.”
The PM once again ruled out engaging in conflict with Russia in Ukraine after being urged by an emotional Ukrainian journalist to enforce a no-fly-zone over her country.
Asked about Daria Kaleniuk's plea, Mr Johnson said: "In order to have a no-fly-zone above Ukraine you would have to take decisions to shoot down Russian jets and that's not something that any western country is contemplating."
"What we can do is stick up for the Ukrainians, support them in the ways that we are, offer humanitarian relief and assistance, and offer to welcome them.
"Though don't forget we also want to have a thriving and prosperous Ukraine after this - so we don't want to trigger a collapse and an exodus from Ukraine, but what we can do is demonstrate to the international community and to Vladmir Putin and above all to the people of Russia that this has been a mistake.”
He said rather than joining the conflict, the UK was extending its visa scheme to more Ukrainians so they can seek refuge in Britain.
The UK could accept 200,000 or more refugees after extending the policy for Ukrainians with immediately family in the UK to include adult parents, grandparents, children over 18 and siblings, the PM said.
And a separate scheme will allow individuals and organisations to sponsor Ukrainian refugees to come to the UK, even if they do not have immediate family settled in Britain.
Mr Johnson told reporters during his visit to Poland that "very considerable numbers would be eligible" to enter the UK - a "couple of hundred thousand, maybe more".
But Home Secretary Priti Patel, updating MPs in the Commons on the latest immigration changes, said the UK cannot waive visas for people fleeing from Ukraine as it must protect national security.
Why has Russia invaded Ukraine and can Putin be stopped?
She said "Russian troops are seeking to infiltrate and merge with Ukrainian forces" and that there are "extremists on the ground" in Ukraine.
She added: "Given this and also Putin's willingness to do violence on British soil, and in keeping with our approach which we have retained consistently throughout all emergency evacuations including in Afghanistan, we cannot suspend any security or biometric checks on people we welcome to our country.
"We have collective duty to keep the British people safe and this approach is based on the strongest security advice."