The Prime Minister is due to fly to Nato’s border with Russia, pledging that Vladimir Putin will “feel the consequences” for invading Ukraine.

Boris Johnson will travel on Tuesday to meet counterparts in Poland and Estonia and visit British troops as he pushes for Western unity in punishing the Russian president for starting a conflict that has taken “hundreds” of lives in only five days.

Before his trip to eastern Europe, the Prime Minister urged allies to “speak with one voice” to ensure “Putin must fail”.

Foreign Secretary Liz Truss will also embark on a diplomatic mission as she prepares to address the United Nations Human Rights Council in Geneva.

The Cabinet minister is expected to tell the council that Mr Putin has “blood on his hands” and that he has been “murdering Ukrainians indiscriminately”.

“Putin is violating international law… he is violating human rights on an industrial scale and the world will not stand for it,” Ms Truss is expected to say in a speech urging the West to “isolate” Russia as a result of the war it has instigated.

The comments are due to be made only 24 hours after Moscow suggested it had put the Russian nuclear deterrent on high alert in response to unspecified comments made by Ms Truss.

The ministerial trips come after the UK Government looked to “up the pressure” on the Kremlin on Monday, with fresh sanctions on Russian banks and Transport Secretary Grant Shapps urging all UK ports to deny access to Russian flagged, registered or operated vessels.

Mr Johnson, in a call on Monday with world leaders from the G7, Nato and the European Union, stressed the need for allies to continue to provide Kyiv with defensive weapons.

He also said Ukraine’s neighbours would require support to deal with “large numbers of Ukrainians escaping violence”.

On Tuesday, the Prime Minister is scheduled to meet with Warsaw and Tallinn leaders and visit British troops serving in Estonia, which shares a border with Russia.

Speaking before his visit to the two Nato members, Mr Johnson said: “Alongside all our international allies the UK will continue to bring maximum pressure to bear on Putin’s regime to ensure he feels the consequences of his actions in Ukraine.

“We speak with one voice when we say, Putin must fail.”

Officials said Mr Johnson will meet Polish Prime Minister Mateusz Morawiecki before travelling on to Estonia, where he will hold talks with Nato secretary general Jens Stoltenberg.

They will jointly visit British troops serving “on the front line of Russian aggression” in Tapa, No 10 said, before meetings with Estonian Prime Minister Kaja Kallas and Estonian President Alar Karis to discuss security.

Ukraine was braced for another evening of attacks, with reports that Kyiv had come under fire on Monday evening.

BBC broadcaster Clive Myrie said he had to take shelter underground after the building he was reporting from in the capital was “shaken by nearby missile fire”.

He tweeted: “Windows shook. Closest blast yet to our base. Fighting coming closer to heart of Kyiv.”

It came after a first round of Ukraine-Russia talks aimed at ending the fighting concluded with no immediate agreements.

Western officials believe that so far around half of the Russian forces that had been ringed around Ukraine’s borders have been committed to the assault on the country.

Moscow could use more indiscriminate force if the invasion stalls, British officials fear.

Meanwhile, in New York, British diplomat Dame Barbara Woodward was part of a chorus of Western pleas for Russia to “stop the war”.

The UK permanent representative to the UN told the Security Council that Russia’s attack had brought Ukraine to the “brink of humanitarian catastrophe” and that only a withdrawal of troops could “save the Ukrainian people from the disaster that Russia is inflicting upon them”.

She said “hundreds of civilians had been killed as a result of the Russian invasion” and seven million people had been displaced, with the figure “rising exponentially”.

The Ukraine’s representative, Sergiy Kyslytsya, told the council that Kyiv was “sitting within Russian crosshairs right now” and that 352 people, including 16 children, had been killed as of Monday in the fighting.

He accused Moscow troops of attacking hospitals and ambulances in a determination to “kill civilians”, adding: “There is no debate. These are war crimes.”

But Vasily Nebenzya, the Russian UN permanent representative, said his country’s armed forces did “not have the goal of occupying Ukraine or harming the local population”.