James Cleverly told Trevor Phillips on Sunday: "Unfortunately, at the moment, an attack, an invasion seems far more likely than unlikely but we will continue to work to try and avert that.

"Everything that we see indicates that invasion is very, very, highly likely and very, very imminent."

Boris Johnson has warned that intelligence suggests Russia is planning "the biggest war in Europe since 1945" and "all the signs are that the plan has already in some senses begun".

"People need to understand the sheer cost in human life that could entail - not just for Ukrainians but for Russians," the prime minister added.

Follow live updates on the Ukraine-Russia crisis

Foreign Secretary Liz Truss has said the West needs to stop Moscow in its tracks - and speaking to The Mail on Sunday, expressed fears that Vladimir Putin "will not stop at Ukraine".

She suggested Russia's president may move to "turn the clock back to the mid-1990s or even before then" by annexing Baltic states including Estonia and Latvia.

World leaders have gathered in Germany in the hope of reaching a diplomatic solution to ever-worsening geopolitical tensions.

At the security conference, UN Secretary-General Antonio Guterres said the current threat to global security is "more complex and probably higher" than during the Cold War.

And he warned that even a small mistake or miscommunication between major powers could have catastrophic consequences.

Read more: How big is Russia's military - and how does it compare with Ukraine?

'Drills in Russia should not worry anyone'

Dmitry Polyanskiy, Russia's deputy ambassador to the UN, told Sky News Russian troops are not on the Ukrainian border and are simply carrying out planned exercises.

"I don't think our drills on our territory should worry anyone," he said.

And he said Ukraine is shelling a "peaceful population" in Donbas, the Ukrainian region Russian-backed rebels took over in 2014 where both sides have accused each other of attacks, prompting the West to accuse Moscow of carrying out a "false flag" operation, in which Russia claims Ukraine is attacking it as a pretext for invasion.

Mr Polyanskiy added that Russia does not trust US and British intelligence about an imminent invasion as he questioned where the West is getting the number of Russian troops amassing near the border from.

He also accused Western leaders of "scaremongering and warmongering" as he denied Mr Putin was enjoying the crisis and said Russia wants to get the West around the negotiating table and "see what we can do for security and guarantees for Russia's absolutely legitimate concerns".

Ukraine's president seeks meeting with Putin

On Saturday, Ukraine's president called for a meeting with his Russian counterpart in search of a resolution to the crisis.

Volodymyr Zelenskyy said the Kremlin could pick where the talks were held, adding: "I don't know what the president of the Russian Federation wants, so I am proposing a meeting."

Read more: Russian disinformation has 'more than doubled' in past week

There has been a sharp spike in violence in and around territory held by Russia-backed rebels, with separatist leaders in eastern Ukraine ordering a full military mobilisation on Saturday.

Mr Zelenskyy appeared frustrated during the conference in Munich, and urged members of the UN Security Council to meet and draw up new security guarantees for his country.

"The rules that the world agreed on decades ago no longer work. They do not keep up with new threats … This is a cough syrup when you need a coronavirus vaccine," he warned.

Read more: Is Russia going to invade - and what does Putin want?

Hundreds of ceasefire violations as loud explosions heard

Almost 2,000 ceasefire violations were registered yesterday by monitors for the Organisation for Security and Cooperation in Europe.

And according to a Reuters reporter, multiple explosions were heard in the early hours of Sunday in the centre of the separatist-controlled city Donetsk.

Top Ukrainian military officials came under a shelling attack during a tour of the front of the separatist conflict and had to flee to a bomb shelter.

Meanwhile, the Kremlin confirmed that Russia had successfully test-launched hypersonic and cruise missiles at sea during nuclear drills.

Washington has accused troops massed near Ukraine's border of being "poised to strike", but US President Joe Biden does not that Mr Putin is remotely contemplating using nuclear weapons.

Read more: Eyewitness - Incoming artillery is more intense

Civilians evacuate as talks continue

Thousands of people are now being evacuated from eastern Ukraine - with Russia's nearby Rostov region declaring a state of emergency as it struggles to cope.

Local reports described chaotic scenes - with long lines for buses and hundreds of people waiting in the cold for hours on end to be housed, without access to food or bathroom facilities.

Mr Putin has ordered the Russian government to offer 10,000 rubles ($130) to each evacuee, which is roughly equivalent to half of an average monthly salary in eastern Ukraine.

According to Russian news agencies, 10,000 evacuees have now arrived in Russia, and separatist leaders have said they intend to evacuate 700,000 people.

One woman who was boarding a bus with her four-year-old daughter said: "It's really scary. I've taken everything I could carry."

The White House says Mr Biden will convene a meeting of the National Security Council later today, and intelligence continues to suggest "Russia could launch an attack against Ukraine at any time".