Ukrainian President Volodymyr Zelenskyy is expected to address the United Nations Security Council Tuesday and likely discuss allegations of war crimes committed by Russia following the discovery of executions and mass graves.

World leaders expressed increasing outrage after seeing reports of dead Ukrainian civilians — many of whom appear to have been executed — strewn about in Bucha, a city northwest of Kyiv. Photos of bodies lining the streets and satellite images of mass graves first surfaced Saturday after Russian forces withdrew from positions outside Ukraine's capital. Having seen the atrocities firsthand, Zelenskyy will address the Security Council Tuesday morning.

Barbara Woodward, the British ambassador to the U.N., told reporters Monday that Tuesday's meeting will require council members to face "the true reality" of the Russia's invasion of Ukraine.

"What's important about this meeting is it will be the first opportunity the Security Council has had to discuss the images that we've seen in Bucha, which you've heard widely over the weekend described both as war crimes and as genocide," Woodward said.

She also said the U.K. "strongly supports" U.S. efforts to suspend Russia's voting rights on the U.N.'s Human Rights Council, championed by Linda Thomas-Greenfield, the U.S. ambassador to the U.N.

"Russia should not have a position of authority in that body, nor should we allow Russia to use their role on the Council as a tool of propaganda to suggest they have a legitimate concern about human rights. In fact, we see every day, including yesterday, heartbreaking reports about how little they care about human rights," Thomas-Greenfield said at a press conference in Romania Monday. "Russia's participation on the Human Rights Council is a farce. It hurts the credibility of the Council and the U.N. writ large. And it is simply wrong. Which is why we believe it is time for the U.N. General Assembly to suspend them."

The U.K.'s Johnson vows to "starve Putin's war machine"

Despite what seems to be overwhelming evidence to the contrary, Russian officials continue to deny any wrongdoing and have called the photos and reports propaganda staged by the west, NPR previously reported. Kremlin spokesperson Dmitry Peskov said Monday that the images have been manipulated, while Russian Foreign Minister Sergey Lavrov called the events in Bucha "staged."

Despite its best efforts, leaders across the globe aren't buying into the Russian narrative. U.K. Prime Minister Boris Johnson swore to do everything within his power to "starve Putin's war machine," promising increased sanctions against Russia and additional humanitarian support for Ukraine.

President Joe Biden also doubled down on his position Monday, calling for additional sanctions and once again branding Putin a war criminal. "This guy is brutal," the president said. "And what's happening in Bucha is outrageous, and everyone's seen it."

In an address made earlier on Tuesday, Zelenskyy said he will push for a thorough accounting of Russian military forces' behavior. He also said that he believes the number of civilians tortured and killed allegedly at the hands of the Russians is far greater than what has been reported. "The occupiers did things that the locals had not seen even during the Nazi occupation 80 years ago," he said.

"The time will come when every Russian will learn the whole truth about who of their fellow citizens killed. Who gave orders. Who turned a blind eye to the murders," Zelenskyy said. "We will establish all this. And make it globally known."

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