British Prime Minister Boris Johnson is heading to eastern Europe amid the crisis in Ukraine, Downing Street said Monday, as it backtracked on a claim that the goal of Western sanctions is to topple Russian President Vladimir Putin. 

Johnson will on Tuesday visit Poland and Estonia, two NATO allies bordering Russia where Britain has been stepping up military support.

London's tough talk was blamed by the Kremlin for provoking Putin into raising the readiness level of Russia's nuclear forces -- a claim dismissed by UK officials as risible.

Johnson's spokesman raised eyebrows when he told a daily briefing that the swingeing set of sanctions imposed by Britain, Europe and the United States was intended "to bring down the Putin regime".

Downing Street said that he had misspoken, and the spokesman had sought to clarify his comments at the briefing: "What we're talking about here clearly is how we stop Russia seeking to subjugate a democratic country. 

"That's been the message throughout." 

In his latest call with Ukraine's President Volodymyr Zelensky on Sunday evening, Johnson praised the "heroic" resistance of Ukrainians, according to Downing Street. 

The prime minister released a further £40 million ($54 million) in humanitarian aid for Ukraine, after giving an emotional address at London's Ukrainian Catholic cathedral.

"Never in all my study, my memory of politics and international affairs, have I seen so clear a distinction between right and wrong, between good and evil, between light and dark," he told the congregation.

"And that is the real reason why Ukraine is our neighbour today," he said, calling Russia's invasion a "colossal mistake".

Refugee debate 

However, the UK government has come under strong pressure from opposition parties for its restrictive stance on refugees from Ukraine, as the European Union debates throwing open its own doors.

In a tweet that was later deleted, junior Home Office minister Kevin Foster had suggested that Ukrainians could apply to come to Britain as seasonal workers, to pick fruit and vegetables.

In a concession, the government said that immediate family members could now join their Ukrainian relatives in Britain.

The opposition Labour party welcomed the concession but said it "should have happened days ago", and urged the post-Brexit government to work with its former partners in the EU on a Europe-wide approach.

While pledging support for the people of Ukraine, Britain has also been turning the financial screw on the Putin regime in concert with its Western allies.

The government is set to introduce legislation to crack down on Russian "dirty money" in the UK economy, and said that Moscow would also find it harder to access its foreign reserves.

In parallel with the EU and United States, Britain is banning its citizens and companies from carrying out transactions with Russia's central bank, finance ministry and sovereign wealth fund.

Rhetoric 'designed to distract

On the military front, Defence Secretary Ben Wallace said Russia's advance into Ukraine was running into trouble.

"There are many reports of Russians either sort of deserting or surrendering," he told BBC radio.

Putin was trying to "flex muscles" by elevating his state of nuclear readiness, Wallace added, in response to the shock announcement by the Kremlin leader on Sunday.

Downing Street and Wallace disowned remarks Sunday by Foreign Secretary Liz Truss, suggesting that British volunteers were free to travel to Ukraine and fight against Russia.

In a Sky News interview, she had also said that "if we don't stop Putin in Ukraine, we are going to see others under threat -– the Baltics, Poland, Moldova, and it could end up in a conflict with NATO".

That remark was cited by Kremlin spokesman Dmitry Peskov for instigating Putin to raise Russia's nuclear readiness level.

But Johnson's spokesman said, "the rhetoric we are seeing from Putin's regime is designed to distract from the situation on the ground".

Russian tycoon Oleg Deripaska on Monday said it was time to put an end to "all this state capitalism" and change policies as the country's economy reeling from the effects of Western sanctions over Moscow's assault on Ukraine.

"It is necessary to change the economic policy, it is necessary to end all this state capitalism," Deripaska said on messaging app Telegram, demanding "explanations" from officials on what was going to happen to the economy in the next three months.

"If this is a real crisis then we need real crisis managers and not fantasists with a bunch of silly presentations," said the 54-year-old.

"Unlike in 2014, it will not be possible to sit this out now," Deripaska said, referring to Moscow's annexation of Ukraine's Crimea peninsula and the subsequent introduction of Western sanctions. 

The billionaire owner of Premier League football club Chelsea, Roman Abramovich, has been involved in ending the crisis, his spokeswoman said.

"I can confirm that Roman Abramovich was contacted by the Ukrainian side for support in achieving a peaceful resolution, and that he has been trying to help ever since," she said. 

"Considering what is at stake, we would ask for understanding as to why we have not commented on neither the situation as such nor his involvement."

The Russian-Israeli billionaire announced on Saturday that he was handing the "stewardship and care" of Chelsea to the trustees of the club's charitable foundation. But he will remain as owner. 

Another billionaire, banker Oleg Tinkov, spoke out directly against the war.

"In Ukraine, innocent people are dying every day, this is unthinkable and unacceptable!" he said on Instagram. 

"States should be spending money on treating people, on research to defeat cancer, and not on war. We are against this war!"

As Western governments tighten their squeeze on Russia's economy following Moscow's invasion of Ukraine, capitals also have their sights on Moscow's wealthy elite and its assets abroad, seen by experts as a way of sapping President Vladimir Putin's power.