(AFP) - Ukrainian President Volodymyr Zelensky challenged the United Nations to "act immediately" or "dissolve yourself altogether" during a blistering address Tuesday in which he showed harrowing footage of dead bodies -- including children -- he said were victims of Russian atrocities.

Likening Russia's actions in Bucha and other Ukrainian cities to violence carried out by "terrorists" such as the Islamic State group, Zelensky called on the 15-member Security Council -- which aims to ensure international peace and security -- to expel Russia "so it cannot block decisions about its own aggression, its own war."

Russia, as one of the five permanent members of the Council, has a veto, which it has repeatedly wielded to block resolutions and negotiations on the global stage.

That means it cannot be expelled from the body, as it would simply veto any vote or recommendation by the Security Council to do so.

"If there is no alternative ... then the next option would be dissolve yourself altogether," Zelensky continued.

"Ladies and gentlemen, are you ready to close the UN? ... If your answer is no, then you need to act immediately."

Bearded and dressed in his now trademark military green T-shirt, Zelensky, speaking remotely from Kyiv, gave a chilling rendition of the atrocities he said were carried out by Russian troops against civilians in Bucha, a town outside the Ukrainian capital.

Bucha had been occupied by Russian troops, but when they withdrew recently Ukrainian authorities and independent international journalists including AFP found bodies of people in civilian clothing, some with their hands tied behind their backs.

Zelensky aired a graphic, 90-second clip of what he said were images from towns including Bucha and the southern port of Mariupol.

The footage showed partially uncovered dead people, including children, in shallow graves, several bodies in a courtyard and dead people with hands tied behind their back slumped towards a wall.

"Now the world can see what the Russian military did in Bucha," Zelensky said.

"They were killed in their apartments, houses, blowing up grenades, civilians were crushed by tanks while sitting in their cars in the middle of the road, just for their pleasure. They cut off limbs... slashed their throats," he said.

"Women were raped and killed in front of their children, their tongues were pulled out only because the aggressors did not hear what they wanted to hear from them.

"This is no different from other terrorists such as Daesh ... and here it is done by a member of the United Nations Security Council," he said, using another acronym for the Islamic State group.

"Accountability must be inevitable," he said, claiming that "hundreds of thousands" of Ukrainians had also been deported to Russia.

Moments later Russia's ambassador, in his own comments, rejected the claims entirely.

- 'No witnesses' -

Addressing his remarks directly to Zelensky, Vassily Nebenzia said Moscow places "on your conscience the ungrounded accusations against the Russian military, which are not confirmed by any eye witnesses."

At least one witness has told AFP of watching Russian soldiers shoot a man in cold blood in Bucha.

Russia has claimed that images presented by Ukrainian authorities to show there had been a massacre in Bucha were fake, or that the deaths occurred after Russian soldiers pulled out of the areas.

It has not offered evidence, and satellite imagery has shown bodies there for weeks, before Moscow withdrew its troops from the town.

Nevertheless Nebenzia repeated those claims, telling the council: "You only saw what they showed you. You couldn't ignore the flagrant inconsistencies in the version of events which are being promoted by Ukrainian and Western media."

He also denied Zelensky's allegation of mass deportations.

Since the invasion began "over 600,000 people have been evacuated to Russia, including over 119,000 children," Nebenzia told the body.

He said the evacuations were "voluntary," not "coercion or abduction."

Russia invaded Ukraine on February 24, sparking outrage across the world and displacing millions of Ukrainians.

© Agence France-Presse