Vladimir Putin is "changing tactics" after the initial "failure" of his attack on Ukraine, the UK defence secretary has told ITV News, with the Russian invasion "way behind schedule".
Ben Wallace said the Russian army "thought that this would be over in a short period of time" but after day seven of the invasion "none of the major objectives have been controlled".
Asked if it was only a matter of time before the takeover of Ukraine is complete, Mr Wallace said "nothing is inevitable" but the Russians have "overwhelming force".
What is Putin's strategy now?
"What's happening is the Russians are changing their tactics," he said, "they've realised their initial plan was a failure and so what we see is night time bombings because they are afraid of anti-air during the day.
"We've seen massive bombardments and potential encirclement rather than actually going into the cities where they know they'll lose thousands of soldiers."
Russian troops have entered Ukraine's second city Kharkiv following days of intensive bombardment, but Mr Wallace said Mr Putin's forces did not yet control it.
On Tuesday, Boris Johnson said Putin had "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.
"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]."
Do Russians want to takeover Ukraine?
The defence secretary told ITV News that one "major miscalculation" made by Putin was that the Russian people may not want an invasion of Ukraine.
He said: "The big miscalculation from President Putin is I think he thought his own population was a population of 40 years ago.
"You cannot control the media, you can shut it down but his own population are just like our families. They have access to social media, they think differently and I think that was a major miscalculation."
Some Russians have been left totally in the dark about the invasion, with civilians and even some soldiers apparently totally oblivious that their country was attacking its neighbour.
A "final message" exchange between a Russian soldier named Alyosha and his mother, read out at the UN General Assembly on Monday, laid bare the difference in narratives being told in Russia and the West.
"Alyosha, how are you doing? Why has it been so long since you responded? Are you really in training exercises?" the soldier's mother wrote.
The soldier replied: "Mama, I'm no longer in Crimea. I'm not in training sessions."
"Where are you then? Papa is asking whether I can send you a parcel."
"Mama, I'm in Ukraine," the soldier said, "There is a real war raging here. I'm afraid. We are bombing all of the cities together, even targeting civilians.
"We were told that they would welcome us and they are falling under our armoured vehicles, throwing themselves under the wheels and not allowing us to pass. They call us fascists. Mama, this is so hard."
Mr Wallace told the BBC Russian troops had been deceived by their leaders and were suffering due to the lack of logistic support, meaning they were low on supplies and food.
"We have definitely seen cases of very quick surrenders by Russian forces, we have seen lots of abandonment of incredible pieces of equipment," he told BBC Radio 4's Today.
"That is what happens when your military leaders don't prepare you, lie to you or deceive you and also you base a military plan based on an arrogant assumption that you are the liberator."
What is the situation in Ukraine now?
The Ministry of Defence said the latest intelligence suggested Russian forces had reportedly moved into the centre of Kherson in south Ukraine.
Artillery and air strikes have targeted built-up areas in Kyiv, Kharkiv, Mariupol and Chernihiv.
The UN human rights office said on Tuesday it had recorded 136 civilian deaths including 13 children, but the real toll is believed to be far higher.
According to the Ukrainian military, the aerial assault began just as air raid sirens were starting to sound in Kharkiv and the surrounding region.
The statement adds the Russian troops attacked a regional military hospital, and that fighting is ongoing.
Downing Street said possible war crimes were occurring "almost hourly" in Ukraine.
Asked whether the PM regarded the Russian attack on the Kyiv holocaust memorial at Babi Yar or the targeting of apartment blocks as war crimes, his official spokesman said: "I think all of those you've listed could fall in that category.
"Obviously, formally it will be for a criminal court to make that ruling but I think no one can be in any doubt that what we're seeing daily, almost hourly now, are horrific acts that would certainly appear to be war crimes."
Mr Wallace told ITV News "years of resistance" to a Russian occupation.
"Invading a country with overwhelming force is one thing, occupying a people of 44 million who don't want you in - it is a very different thing."