WARNING: READERS MAY FIND IMAGES IN THIS STORY DISTURBING

International outrage is growing after independent international journalists filmed corpses in civilian clothes, some with their hands bound, in the town of Bucha outside Ukraine's capital after Kyiv's forces retook it from Russia's army.

Visiting the scene on Monday, Ukrainian President Volodymr Zelenskyy said "these are war crimes and it will be recognised by the world as genocide."

Russia dismissed the videos as "fake" and asked for a United Nations Security Council meeting to discuss what Moscow has called "Ukrainian provocations" in the town.

Ukrainian prosecutor general Iryna Venediktova said 410 civilian bodies had been recovered so far in Bucha and nearby towns.

What Ukraine is saying

A grim-faced Zelenskyy told reporters at the scene "these are war crimes and will be recognized by the world as genocide."

He added: "We know of thousands of people killed and tortured, with severed limbs, raped women and murdered children."

Zelenskyy said the revelations had made it harder for Ukraine to negotiate with Russia. "It's very difficult to talk when you see what they've done here," he said.

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Ukrainian Prosecutor General Iryna Venediktova said on Monday many acts by Russian forces were classifiable as crimes against humanity, and in this context Ukraine was investigating their actions in areas of the Kyiv region.

Speaking on national television, Venediktova said the situation in the town of Borodyanka was the worst in the Kyiv region in terms of the number of victims. She gave no further details.

Foreign minister Dmytro Kuleba said the incidents amounted to a "massacre" and labeled it "the most outrageous atrocity of the 21st century." He added: "By what we have seen in Bucha and vicinity, we can conclude that Russia is worse than ISIS in the scale and ruthlessness of the crimes committed."

Kuleba said Ukraine was collecting evidence and would work with "all international institutions relevant, to identify and bring those responsible for these crimes to account."

Russia's reaction

The Kremlin has denied that Russian forces killed civilians. Foreign Minister Sergei Lavrov told a news conference Ukraine's version of what happened in the town of Bucha was a "fake attack" aimed at undermining Moscow.

Lavrov told reporters: "Russian military had left the town completely on March 31. On March 31, Bucha's mayor solemnly stated that everything is settled, and two days later we saw that staging on streets which is being used now to undermine Russia."

He added that the video "is now being spread through all media channels and social media by the Ukrainian representatives and their Western patrons."

On a conference call to reporters, Kremlin spokesperson Dmitry Peskov insisted that Russian experts "have identified signs of video falsification." He urged international leaders not to rush to judgment and said Russia's diplomats would press on with their efforts to convene a UN Security Council meeting to discuss the allegations.

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

"I got into trouble with calling Putin a war criminal. The truth of the matter is he is a war criminal but we have to gather the information, we have to provide Ukraine with the weapons they need to continue the fight, and we have to gather all the details so we can have a war crimes trial." – Joe Biden, U.S. President

"I am deeply shocked by the images of civilians killed in Bucha, Ukraine. It is essential that an independent investigation leads to effective accountability." – António Guterres, United Nations Secretary-General

"The murder of civilians is a war crime. We must relentlessly investigate these crimes committed by the Russian armed forces. I demand that international organizations such as the International Committee of the Red Cross be given access to these areas to document the atrocities. The perpetrators and those in charge of them must be held accountable." – Olaf Scholz, German Chancellor

"Yet again the Kremlin is showing its true face, targeting, murdering civilians, destroying civilian infrastructure, violating international humanitarian law and committing war crimes… The Russian authorities are responsible for these crimes, for these violations, and the perpetrators of all these violations and war crimes will be held accountable." – Peter Stano, Spokesman for EU Foreign Policy Chief Josep Borrell

"The scenes are unbearable… We are all extremely shocked, and we have very firmly condemned this. There are very clear signs today pointing to war crimes. It's the Russian army that was in Bucha. We have also signaled to the Ukrainian authorities our willingness to assist them in the investigations they are currently conducting." – Emmanuel Macron, French President

"We can't help but see these images as a punch in the gut… I think the most important thing is we can't become numb to this. We can't normalize this. This is the reality of what's going on every single day as long as Russia's brutality against Ukraine continues." – Antony Blinken, U.S. Secretary of State

"The images of civilians lying dead on the streets and in improvised graves in the town of Bucha in Ukraine are horrifying. Reports emerging from this and other areas raise serious and disturbing questions about possible war crimes, grave breaches of international humanitarian law and serious violations of international human rights law." – Liz Throssell, spokeswoman for the office of the UN High Commissioner For Human Rights

"These bloody massacres committed by Russian soldiers deserve to be called by their name. This is genocide, and must be judged [as such]. This crime scene must be judged as a place of genocide." – Mateusz Morawiecki, Polish Prime Minister 

"The discovery of more mass graves outside Kyiv is sickening. The UK will not stand by whilst this indiscriminate and unforgivable slaughter takes place." – Boris Johnson, UK Prime Minister

"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… 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." – Linda Thomas-Greenfield, U.S. Ambassador to the UN