Amid claims that horrific weapons are now being unleashed by Russian forces, Justice Secretary Dominic Raab issued the stark warning that those responsible for war crimes will be dragged before a court as Nazi leaders were at the Nuremberg trials after the Second World War.
He stressed that all breaches of the laws of war will be documented and recorded.
He told Times Radio: “The ICC (International Criminal Court) prosecutor in The Hague has already said that he is looking at this.
“And the UK in whatever form is necessary will play its role, as we have done over many years since right way back to Nuremberg, to make sure that anyone committing these egregious crimes will be held to account.
“We have shown that recently, Radovan Karadzic, the butcher of the Balkans, has ended up in a British cell, via the Hague for his actions.
“Therefore the seed of doubt must be laid, not just in Putin’s mind, but anyone following these reckless orders and engaged in these reckless attacks on civilians, that they could end up in the dock of a court and they could end up spending the rest of their days behind bars.”
Mr Raab made clear that Mr Putin himself could be brought to court for war crimes.
The Deputy Prime Minister, a human rights lawyer before becoming an MP, told Sky News that it must be clear “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”.
He stressed that the Russian president may resort to “even more barbaric tactics” as his invasion plans were “stuttering”.
Mr Raab stressed: “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.”
He issued the warning as Boris Johnson was flying to Nato’s border with Russia, pledging that Mr Putin will “feel the consequences” for invading Ukraine.
The Prime Minister was due to meet his counterpart 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.
Prior to his trip to eastern Europe, the Prime Minister urged allies to “speak with one voice” to ensure “Putin must fail”.
Foreign Secretary Liz Truss is also embarking 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.
At an emergency meeting of the United Nations Security Council, Ukraine’s representative, Sergiy Kyslytsya, accused Russian forces of a war crime in their assault on the eastern city of Kharkiv.
He also told the council that the capital 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.”
Ukrainian President Volodymyr Zelensky echoed Mr Kyslytsya’s statements in a late-night address on Monday.
In a video posted to social media, the leader said that in five days Russian forces had launched 56 missile strikes and 113 cruise missiles in Ukraine.
He added: “Today, Russian forces brutally fired on Kharkiv from jet artillery. It was clearly a war crime.
“Kharkiv is a peaceful city, there are peaceful residential areas, no military facilities. Dozens of eyewitness accounts prove that this is not a single false volley, but deliberate destruction of people: the Russians knew where they were shooting.”
“There will definitely be an international tribunal for this crime – it’s a violation of all conventions. No one in the world will forgive you for killing peaceful Ukrainian people,” he said.
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”.
But Mr Khan, the chief prosecutor of the International Criminal Court, said he plans to open an investigation “as rapidly as possible” into possible war crimes and crimes against humanity in Ukraine, with reports of cluster and possibly vacuum bombs being used.