Dominic Raab has warned the Russian president Vladimir Putin could resort to “more barbaric tactics” in Ukraine amid fierce resistance on the ground.

       On the sixth day of the invasion, the deputy prime minister claimed the Russian advance had “stuttered” and suggested the conflict was turning into a “much more perilous misadventure” than Putin had anticipated.

       He also insisted that the Russian president and his commanders must be held accountable for any war crimes, as Britain’s UN ambassador warned Ukraine was on the brink of a “humanitarian catastrophe”

       His remarks came after an intelligence update from the Ministry of Defence (MoD) said the Russian advance on Ukraine’s capital, Kyiv, has made “little progress” in the last 24 hours.

       However, there were reports on Tuesday that the Kremlin was advancing with a huge military convoy of armoured vehicles, tanks and other military equipment spanning more than 40 miles.

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       Speaking on Sky News, Mr Raab said: “We know that Putin will react to this, or we fear that he will react to this, with even more barbaric tactics, that’s why we must be prepared that this could be a long haul.”

       “This is turning into a much, much more perilous misadventure for Putin than I think he realised and it has a demoralised effect on Russia forces and it has had the effect of steeling the will of the Ukrainian people.

       “That’s how we will ensure Putin fails in Ukraine and we’re there for the long haul.”

       Pressed on British intelligence assessments on how long Kyiv could withstand the Russian assault, Mr Raab added: “I’m not going to comment directly on the intelligence we get.

       The map shows the extent of Russia’s invasion of Ukraine

       (Press Association Images)

       “But it’s very difficult to say. The Russian initial advance has been slowed down more than they expected and that’s a testament to the Ukrainian fortitude and courage.”

       The deputy prime minister went on: “If Putin occupies Kyiv or one of the other major cities, that doesn’t mean this is over. I think what you’re seeing is Ukrainians bedding down for some form of guerrilla challenge which will take a lot longer and could well be unresolvable from the point of view of Putin’s military objective”.

       Mr Raab also warned that Putin and his commanders must be held accountable for any war crimes during Moscow’s siege on Ukraine, saying: “Those that engage in war crimes will be held to account.

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       He said it must be clear to “both to Putin but also to commanders in Moscow and on the ground in Ukraine that they will be held accountable for any violations of the laws of war”.

       On Putin himself, he added: “That is there as well. He is ultimately the person in charge by command and responsibility. That is very much a factor and this ought to play into his calculations”.