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UK Prime Minister Boris Johnson has said "we will not rest until justice is done", amid further evidence of continued atrocities in Ukraine.
Distressing images of civilian bodies in the streets of Bucha, near Kyiv, have led to international outrage over Russia's actions.
The UK is expected to push for tougher international sanctions on Russia.
Foreign Secretary Liz Truss is meeting her Ukrainian counterpart in the Polish capital Warsaw.
A senior Westminster source has told the BBC the government is considering further action against Russian soldiers as individuals.
Officials are looking at further sanctions that could target captains, majors and colonels in the Russian military.
It is understood this additional pressure could also include looking at ways to hold Russian soldiers legally accountable.
Mr Johnson has said the UK "will not stand by whilst this indiscriminate and unforgivable slaughter takes place".
He added: "We are working to ensure those responsible are held to account. We will not rest until justice is done."
Ukrainian authorities said the bodies of 410 civilians have been found in the areas around Kyiv so far.
Russia, without evidence, has said the photos and videos were "a staged performance" by Ukraine.
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Ms Truss will meet with Ukraine's Foreign Secretary Dmytro Kuleba in Poland ahead of key G7 and Nato talks.
The foreign secretary will also hold talks with her Polish counterpart, Zbigniew Rau, on Tuesday. She has pledged a £10m civil society fund for Ukraine, including support for organisations dealing with sexual violence, following reports of Russian forces sexually assaulting people in Ukraine, as a way of terrorising the population.
Ms Truss has said Russia's President Vladimir Putin "is yet to show he is serious about diplomacy". She said "a tough approach from the UK and our allies is vital to strengthen Ukraine's hand in negotiations".
She added the UK would do more "to ramp up the pressure" on Russia and "keep pushing others to do more".
On Sunday, Mr Johnson said Russia's "despicable attacks" on innocent Ukrainian civilians in Bucha and Irpin were "yet more evidence" of war crimes.
Mr Johnson spoke to Ukrainian President Volodymyr Zelensky over the weekend. Following their conversation on Saturday evening, Mr Zelensky said there would be a "new package" of "very, very tangible support".