Vladimir Putin and his forces have been accused of war crimes by the UK and allies after a wave of missile and drone attacks on Ukrainian cities.
Prime Minister Liz Truss and allies from the G7 democracies condemned the strikes in the “strongest possible terms”, adding that “indiscriminate attacks on innocent civilian populations constitute a war crime”.
Russia launched a further wave of missile and drone strikes on Tuesday, hitting power plants and civilian areas across Ukraine.
The blasts followed a barrage which killed 19 and injured scores more in cities including Ukraine’s capital Kyiv on Monday.
After crisis talks the G7 leaders issued a statement vowing to “hold President Putin and those responsible to account”.
The group rejected the “illegal attempted annexation” of four areas of Ukraine and vowed to step up sanctions against Moscow.
“We have imposed and will continue to impose further economic costs on Russia, including on individuals and entities – inside and outside of Russia – providing political or economic support for Russia’s illegal attempts to change the status of Ukrainian territory,” the G7 statement said.
The leaders also warned Moscow that any use of chemical, biological or nuclear weapons would have “severe consequences”.
Ukraine’s President Volodymyr Zelensky addressed leaders from the G7 – the US, the UK, Canada, Japan, France, Germany, Italy and the European Union – at the virtual meeting on Tuesday.
They assured him they remain “undeterred and steadfast” in their support for his nation.
“We will continue to provide financial, humanitarian, military, diplomatic and legal support and will stand firmly with Ukraine for as long as it takes,” they said.
The G7 also said any “just peace” should include respect for Ukraine’s territorial integrity and sovereignty and could also include reparation funding from Russia.
The shift in the Kremlin’s strategy to attacks on civilian areas and infrastructure followed Ukraine’s strike against the strategically and symbolically important Kerch Bridge linking Russia to the annexed Crimean peninsula.
Downing Street said on Tuesday that Ms Truss still hoped to visit Ukraine “as soon as possible”.
The head of the GCHQ intelligence agency said Mr Putin’s regime was becoming increasingly desperate as it ran short of weapons, allies and troops.
Sir Jeremy Fleming said Moscow still had a “very capable military machine” despite the shortcomings, although it was being stretched by the conflict.
Mr Putin has warned about the potential use of nuclear weapons to defend Russian territory – a definition which he could extend to the occupied regions of Ukraine.
Sir Jeremy said he hoped the UK would see “indicators” from Russia before any deployment of nuclear weapons, which would be a “catastrophe”.
He told BBC Radio 4’s Today programme: “We believe that Russia is running short of munitions, it’s certainly running short of friends and we have seen, because of the declaration for mobilisation, that it is running short of troops.”
Sir Jeremy said Moscow’s commanders were “worried about the state of their military machine”, adding: “The word I have used is ‘desperate’ and we can see that desperation at many levels inside Russian society and inside the Russian military machine.”
Pressed on whether GCHQ would know if Mr Putin was considering using nuclear weapons, Sir Jeremy said: “I think any talk of nuclear weapons is very dangerous and we need to be very careful about how we are talking about that.
“It’s clear to me that whilst we might not like and in many, many ways abhor the way in which the Russian military machine and President Putin are conducting this war, they are staying within the doctrine that we understand for their use, including for nuclear weapons.
“I would hope that we would see indicators if they started to go down that path, but let’s be really clear about that: if they are considering that, that would be a catastrophe in the way that many people have talked about.”
In the Commons, defence minister Alec Shelbrooke was pressed to say what the UK response would be to use of nuclear weapons.
“President Putin should be clear that for the UK and our allies, any use at all of nuclear weapons would break a taboo on nuclear use that has held since 1945 and would lead to severe consequences for Russia,” Mr Shelbrooke said.
Meanwhile, Justice Secretary Brandon Lewis had his first meeting in the role with International Criminal Court (ICC) prosecutor Karim Khan KC.
Mr Lewis said the pair discussed “the atrocities in Ukraine, including this week’s bombing of civilian targets” and ongoing co-operation between the UK and the ICC.
