US President Joe Biden says Vladimir Putin should be tried for war crimes as international condemnation grows over the Russian military killing hundreds of civilians in towns around Kyiv.

Without mincing words, Mr Biden said “he is a war criminal” but the president added “we have to gather evidence”.

“This guy is brutal and what’s happening to Bucha is outrageous, and everyone sees it,” said Mr Biden.

Mr Biden said he would consider further sanctions as the pictures that have emerged from the town look set to galvanise the US and Europe into fresh sanctions against Moscow.

It comes as Ukraine’s President Volodymr Zelensky visited Bucha, northwest of Kyiv, and walked the streets where the bodies of civilians had earlier been found littering the streets after Russian troops retreated at the weekend.

Wearing a flak jacket and addressing cameras, a graved-faced Mr Zelensky said the Russian soldiers’ treatment of human beings was “worse than animals”.

He said while Ukrainians had shown humanity towards even the plight of stray pets in the war by seeking food for the animals, the Russian military showed no respect for human life.

“That’s a characteristic trait of our people, I think — treat animals the way you would treat humans,” he said.

“You can see around what was done to this modern town. That’s a characteristic of Russian soldiers – treat people worse than animals. That is real genocide, what you have seen here today.”

Ukrainian President Volodymyr Zelensky visits the town of Bucha, after it was liberated from the Russian Army. Photo: Getty

Meanwhile Ukraine’s prosecutor-general Iryna Venediktova said the bodies of 410 civilians had been removed from Kyiv-area towns that were recently retaken from Russian forces.

Ukraine’s Foreign Minister Dmytro Kuleba told the BCC’s Hardtalk program the Bucha “massacre” should remove any hesitation in the West about giving Ukraine the weapons and support it needs to defend itself.

“I’m ready to exchange every word of sympathy and admiration for a tank or a plane that will help me, or or an embargo on gas and oil that will help me to save human lives in Ukraine,” he said.

But he said the shocking discoveries in Bucha, where people seemed to have been shot indiscriminately on the streets, were “just the tip of the iceberg”  and that the situation was worse in Mariupol.

Tens of thousands of civilians remain trapped in the besieged port city which has been virtually reduced to rubble. Because of the high Russian presence there, the Red Cross has had trouble evacuating people to safety.

“I can tell you without exaggeration, but with great sorrow, that the situation in Mariupol is much worse,” said Mr Kuleba.

War crimes investigations

As evidence of Russian atrocities becomes more evident, the EU has offered to undertake a joint investigation with Ukraine.

EU Commission President Ursula von der Leyen offered Mr Zelensky her condolences on the “dreadful murders” that the world witnessed in “harrowing mages”.

“The EU is ready to reinforce this effort by sending investigation teams on the ground to support the Ukrainian Prosecution Services,” she said.

The US and more than 40 other countries are working together to investigate possible violations and abuses, after the passage of a resolution by the United Nations Human Rights Council to establish a commission of inquiry.

There is another probe by the International Criminal Court, an independent body based in the Netherlands.

Human Rights Watch said it had documented “several cases of Russian military forces committing laws-of-war violations” in the Ukrainian regions of Chernihiv, Kharkiv and Kyiv.

The discovery of more mass graves outside Kyiv is sickening. The UK will not stand by whilst this indiscriminate and unforgivable slaughter takes place.

We are working to ensure those responsible are held to account.

We will not rest until justice is done.

— Boris Johnson (@BorisJohnson) April 4, 2022

Meanwhile, Mr Biden’s chief envoy to the United Nations, Ambassador Linda Thomas-Greenfield, said the US would seek a suspension of Russia from its seat on the UN’s top human rights body.

Russia is in its second year of a three-year term on the Geneva-based council.

A two-third majority vote by the 193-member assembly in New York can suspend a state from the council for persistently committing gross and systematic violations of human rights during its membership.

Speaking in Bucharest on Monday, Mr Thomas-Greenfield said: “Russia’s participation on the Human Rights Council is a farce.

“And it is wrong, which is why we believe it is time the UN General Assembly vote to remove them.”

Since the Ukraine invasion began on February 24, the UN General Assembly has adopted two resolutions denouncing Russia with at least 140 yes votes.

“My message to those 140 countries who have courageously stood together is: the images out of Bucha and devastation across Ukraine require us to now match our words with action,” said Mr Thomas-Greenfield, visiting Romania to see how the country was coping with an influx of Ukraine refugees.

Russia flatly denies killings

Moscow has reacted to the world’s condemnation by saying the killings in Bucha there were “staged” to sully Russia’s name.

Kremlin spokesperson Dmitry Peskov said its diplomats would press on with efforts to convene a Security Council meeting to discuss what Moscow has called “Ukrainian provocations” in the town.

The facts and chronology did not support Ukraine’s version of events there, Mr Peskov told reporters, urging international leaders not to rush to judgment.

Russia has denied targeting civilians and has rejected allegations of war crimes.

Mr Peskov declined to comment on whether the furore over Bucha would affect peace talks between Moscow and Kyiv, which had been set to resume via video conference on Monday.

Mr Zelensky said peace talks were still on the table.

-with AAP