Ukrainian President Volodymyr Zelenskyy said on Monday night that he will address the United Nations Security Council on Tuesday, reported the Reuters news agency.
Zelenskyy said that in Bucha, where mass graves and bodies were found after Ukraine took the town back from Russian forces, at least 300 civilians have been killed, and he expects that in Borodyanka and other towns the number of casualties may be even higher.
"I would like to emphasize that we are interested in the most complete, transparent investigation, the results of which will be known and explained to the entire international community," the Ukrainian President said in his nightly video address.
Zelenskyy spoke on national television earlier on Monday and said it had become harder for his country to negotiate with Russia since Kyiv became aware of the scale of atrocities carried out by Russian troops in Ukraine.
"These are war crimes and will be recognized by the world as genocide," Zelenskyy said during a visit to Bucha.
"It's very difficult to talk when you see what they've done here," he added. "The longer the Russian Federation drags out the negotiating process, the worse it is for them and for this situation and for this war."
"We know of thousands of people killed and tortured, with severed limbs, raped women and murdered children," he said.
Zelenskyy’s comments come a day after footage showed hundreds of bodies in the Kyiv suburb of Bucha as Ukrainian forces retook areas previously occupied by the Russian army.
Germany, France, Britain, the US, and the European Union condemned Russia following the discoveries, with France, Britain, and Germany calling for a war crimes investigation.
On Monday, US President Joe Biden called Russian President Vladimir Putin a "war criminal" and called for him to be put on trial following reports of the mass graves in Bucha.
“He is a war criminal,” Biden told reporters. “This guy is brutal, and what’s happening in Bucha is outrageous and everyone’s seen it."
“I think it is a war crime," he added. "He should be held accountable.”