British Prime Minister Boris Johnson on Sunday condemned alleged mass killings of civilians by Russian forces as they withdrew from Ukrainian towns and cities.
Johnson said his government would do everything it could to thwart Russia in its war with Ukraine and to support Kyiv.
"Russia's despicable attacks against innocent civilians in Irpin and Bucha are yet more evidence that Putin and his army are committing war crimes in Ukraine," the prime minister said.
"No denial or disinformation from the Kremlin can hide what we all know to be the truth -- Putin is desperate, his invasion is failing, and Ukraine's resolve has never been stronger," Johnson added.
He underlined that his government would enlarge its sanctions regime against Moscow and provide more military support to Kyiv, along with humanitarian aid to displaced Ukrainians in the country.
"I will do everything in my power to starve Putin's war machine. We are stepping up our sanctions and military support, as well as bolstering our humanitarian support package to help those in need on the ground."
"The UK has been at the forefront of supporting the International Criminal Court's investigation into atrocities committed in Ukraine, and the Justice Secretary has authorized additional financial support and the deployment of specialist investigators -- we will not rest until justice is served."
Earlier on Sunday, the UK's Foreign Secretary Liz Truss condemned Russian atrocities committed in the cities of Irpin and Bucha, from which Russian forces recently withdrew. Truss called for an international investigation on the killings and for them to be treated as war crimes.
Images from Bucha, located near the capital Kyiv, purport to show civilian bodies laying in the streets. Residents who spoke to Sky News said the civilians were shot dead by retreating Russian troops without provocation, their hands and feet later discovered to have been tied and bound.
International condemnations have grown since the photos and footage surfaced, drawing the condemnation of German and French leaders.
Ukrainian Foreign Minister Dmytro Kuleba called on the international organizations on Sunday to send their experts to the country as soon as possible to collect evidence of war crimes committed by the Russian troops.
Meanwhile, the Russian Defense Ministry has denied that its troops killed civilians while withdrawing from towns near Kyiv.
The Russian war against Ukraine, which started on Feb. 24, has been met with international outrage, with the EU, US, and Britain, among others, implementing tough financial sanctions on Moscow.
At least 1,417 civilians have been killed in Ukraine and 2,038 injured, according to UN estimates, with the true figure feared to be far higher.
More than 4.2 million Ukrainians have also fled to other countries, with millions more internally displaced, according to the UN refugee agency./aa