The hands of one man are tied behind his back with a piece of white cloth. Another man lies alone, tangled up in a bicycle by a grassy bank. A third man lies in the middle of the road, near the charred remains of a burned-out car.

The shocking images of the carnage in Bucha were captured by Agence France-Presse on Saturday, the same day Ukraine declared the town liberated from Russian troops. Accounts of alleged Russian atrocities are emerging as its forces retreat from areas near Kyiv following a failed bid to encircle the capital.

The town of Bucha has endured five weeks of near-constant firefights. Now officials and human rights groups are blaming the civilian deaths on the departed Russian forces.

"Corpses of executed people still line the Yabluska street in Bucha. Their hands are tied behind their backs with white 'civilian' rags, they were shot in the back of their heads. So you can imagine what kind of lawlessness they perpetrated here," Bucha mayor Anatoliy Fedoruk told Reuters on Saturday.

In a video address Sunday after the reports out of Bucha, Ukrainian President Volodymyr Zelensky called for an end of Russian "war crimes."

"The world has already seen many war crimes. At different times. On different continents. But it is time to do everything possible to make the war crimes of the Russian military the last manifestation of such evil on earth," he said.

Zelensky called on Russian leaders to be held accountable for the actions of the nation's military.

"I want all the leaders of the Russian Federation to see how their orders are being fulfilled. Such orders. Such a fulfillment. And joint responsibility. For these murders, for these tortures, for these arms torn off by explosions that lie on the streets. For shots in the back of the head of tied people. This is how the Russian state will now be perceived. This is your image," Zelensky said.

The alleged atrocities in Bucha have drawn international outrage, with Western leaders, including US Secretary of State Antony Blinken, calling for war crimes investigations and increasing sanctions on Russia.

CNN has not been able to independently confirm the details around the men's deaths.

In his address, Zelensky announced a "mechanism of justice" would be established to investigate crimes committed by Russian soldiers in Ukrainian territory. The mechanism would be supported by the Ministry of Foreign Affairs, the Prosecutor General's Office, the National Police, the Security Service, the Intelligence Service and other government branches, he said.

"This mechanism will help Ukraine and the world bring to concrete justice those who unleashed or in any way participated in this terrible war against the Ukrainian people and in crimes against our people," he said.

Zelensky said he will provide more information on the state of Ukrainian territory that was occupied by Russian forces.
"All partners of Ukraine will be informed in detail about what happened in the temporarily occupied territory of our state. War crimes in Bucha and other cities during the Russian occupation will also be considered by the (United Nations) Security Council on Tuesday," he said.

He also noted that efforts are underway to restore electricity and water to Bucha, as well as reestablishing medical institutions and infrastructure.

Zelensky once again invoked the need for stronger sanctions against Russia.

"There will definitely be a new package of sanctions against Russia. But I'm sure that's not enough. More conclusions are needed. Not only about Russia, but also about the political behavior that actually allowed this evil to come to our land," he said.

Asked during an appearance earlier Sunday on CBS' "Face the Nation" if Russia was carrying out genocide in his country, Zelensky said: "Indeed. This is genocide."

"The elimination of the whole nation, and the people. We are the citizens of Ukraine. We have more than 100 nationalities. This is about the destruction and extermination of all these nationalities," he said.

The Russian Ministry of Defense has claimed the extensive footage of Bucha was "fake," saying "not a single local resident suffered from any violent actions" during Russia's occupation of the city. "In the settlements of the Kiev region, Russian military personnel delivered and issued 452 tons of humanitarian aid to civilians," it said in a statement.
A separate statement claimed the footage was staged.

"Stories about Bucha appeared in several foreign media outlets at once, which looks like a planned media campaign," the statement said. "Taking into account that the troops left the city on March 30, where was the footage for four days? Their absence only confirms the fake."

The Russian government has consistently responded to allegations of civilian casualties inflicted by Russian forces with blanket denials. After the Russian air force bombed a maternity hospital on March 9, Russian officials attempted to cast doubt on widespread media reports, with one Russian diplomat accusing a victim of the bombing -- a woman who escaped from the bombing, bloodied and still pregnant -- of being an actor and not a real victim.

Mass grave
The toll of the Russian invasion was apparent at a mass grave in Bucha. People cried as they attempted to locate the bodies of lost loved ones at a grave located in the grounds of the Church of St. Andrew and Pyervozvannoho All Saints on Sunday, according to a CNN team at the scene.

Bucha residents told CNN that bodies were first buried in the grave in the first few days of the war. They believe 150 people are buried in the site, many of whom were civilians killed in the fighting around Bucha.

CNN saw at least a dozen bodies in body bags piled inside the grave. Some were already partially covered.

The mayor of Bucha said in public remarks Saturday that up to 300 victims could be buried at the site.

CNN was unable to independently verify those numbers or the identities and nationalities of those buried in the grave.

The earth on the church grounds appeared to have been recently moved so it is feasible that more bodies could be buried there.

Ukrainian presidential adviser Oleksiy Arestovych said Sunday that reports emerging from towns in the Kyiv region revealed a "post-apocalyptic picture" of life under Russian occupation.

"This is a special appeal aimed at drawing the world's attention to those war crimes, crimes against humanity, which were committed by Russian troops in Bucha, Irpin and Hostomel," Arestovych said. "These are liberated cities, a picture from horror movies, a post-apocalyptic picture."

"Victims of these war crimes have already been found, including raped women who they tried to burn, local government officials killed, children killed, elderly people killed, men killed, many of them with tied hands, traces of torture and shot in the back of the head. Robberies, attempts to take gold, valuables, carpets, washing machines. It, of course, will be taken into account by the Prosecutor's Office of Ukraine and law enforcement agencies and international criminal courts."

The evidence of apparent atrocities in Bucha came as Human Rights Watch (HRW) announced it had documented allegations of war crimes in the occupied areas of the Kyiv, Chernihiv and Kharkiv regions.

HRW said Sunday that the allegations include "a case of repeated rape; two cases of summary execution, one of six men, the other of one man; and other cases of unlawful violence and threats against civilians between February 27 and March 14, 2022."

In Bucha, Russian forces "rounded up five men and summarily executed one of them" on March 4, HRW wrote. A witness told the group that soldiers forced the men to kneel on the road and pulled their shirts over their heads, before shooting one of the men in the back of the head.

HRW also alleges that on February 27, six men were rounded up in the village of Staryi Bykiv in the Chernihiv region and later executed.

In Malaya Rohan, a village in the Kharkiv region, a Russian soldier repeatedly raped a woman in a school where she was sheltering with her family on March 13, the victim told HRW. "She said that he beat her and cut her face, neck, and hair with a knife," HRW wrote. The woman fled to Kharkiv the following day, "where she was able to get medical treatment and other services."

And in the village of Vorzel, 31 miles northwest of Kyiv, Russian soldiers "threw a smoke grenade into a basement, then shot a woman and a 14-year-old child as they emerged from the basement, where they had been sheltering," HRW said.

"The cases we documented amount to unspeakable, deliberate cruelty and violence against Ukrainian civilians," Hugh Williamson, HRW's Europe and Central Asia director, said in the statement. "Rape, murder, and other violent acts against people in the Russian forces' custody should be investigated as war crimes."

CNN has not independently verified the details of the HRW report and has requested comment from the Russian defense ministry.

Sunday's developments in Ukraine have hastened calls for war crimes investigations.

Blinken said the State Department would help document any atrocities the Russian military committed against Ukrainian civilians.

"You can't help but see these images as a punch to the gut," he told CNN's Dana Bash on "State of the Union" Sunday, when asked about the civilian killings in Bucha.

"Since the aggression, we've come out and said that we believe that Russian forces have committed war crimes, and we've been working to document that, to provide the information we have to the relevant institutions and organizations that will put all of this together. And there needs to be accountability for it."

UK Foreign Secretary Liz Truss said in a statement Sunday that "indiscriminate attacks against innocent civilians during Russia's illegal and unjustified invasion of Ukraine must be investigated as war crimes."

European Union Council President Charles Michel vowed further sanctions on Russia, while United Nations Secretary-General António Guterres said an "independent investigation" into the civilians killed in Bucha was "essential."