An ex-chief prosecutor for the United Nations is calling for an international arrest for Russian President Vladimir Putin over the "war crimes" his forces committed in Ukraine.

Former UN chief prosecutor Carla Del Ponte has labeled Russian President Vladimir Putin a "war criminal" for the atrocities his forces have caused and continue to cause in various cities in Ukraine. Del Ponte is now calling for the international arrest warrant for the Russian leader.

According to Fox News, Del Ponte was interviewed on Saturday by the Swiss newspaper Le Temps, marking the release of her latest book. The former UN prosecutor, who oversaw investigations in Rwanda and the former Yugoslavia said that Putin was clearly committing war crimes in Ukraine. She was particularly shocked at how the Russian war was using mass graves, which called to mind the violent wars in Yugoslavia.

"I hoped never to see mass graves again," Del Ponte told the newspaper Block. "These dead people have loved ones who don't even know what's become of them. That is unacceptable."

Del Ponte also identified other war crimes by Russia, specifically the attacks on civilians, the destruction of civilian villages, and the wiping out of entire villages. The former UN prosecutor believes that an investigation in Ukraine would be easier than in Yugoslavia as Ukrainian leaders have requested for an international probe. ICC chief prosecutor Karim Khan already visited Ukraine in March. In the event that the ICC finds proof of war crimes, Del Ponte said, "you must go up the chain of command until you reach those who took the decisions."

Del Ponte added that it would be possible to question Putin, just as Serbian President Slobodan Milosevic was investigated while he was in office. In the early 2000s, Milosevic  was arrested and charged with war crimes after launching a brutal campaign of ethnic cleansing against non-Serbians following the collapse of Yugoslavia.

Meanwhile, Human Rights Watch (HRW) on Sunday said it had documented "apparent war crimes" committed by Russian forces against Ukrainian civilians, Reuters reported. In a statement, HRW said that it had found "several cases of Russian military forces committing laws-of-war violations" in Ukrainian cities of Chernihiv, Kharkiv and Kyiv, which are under Russian control.

The statement that was published in Warsaw came after photographs and reports of civilians lying lifeless on the streets of the country town of Bucha near Kyiv in Ukraine were released. The dead bodies were what remained three days after the Russian army retreated after a month-long occupation.

On Sunday, however, Russia's defense ministry denied that its military killed civilians in Bucha. Instead, they insisted that the Russian forces left Bucha on March 30 and that the reports and photographs of dead bodies were "yet another provocation."

But the New York-based HRW claimed it interviewed 10 individuals including witnesses, victims, and local residents in person and over the phone, who revealed the real situation on the ground in Bucha. HRW's Europe and Central Asia director Hugh Williamson said, "The cases we documented amount to unspeakable, deliberate cruelty and violence against Ukrainian civilians."

"Rape, murder, and other violent acts against people in the Russian forces' custody should be investigated as war crimes," Williamson reported. He added that the war crimes committed by Russian troops include one case of repeated rape, two cases of summary execution, and other cases of "unlawful violence and threats against civilians" committed between February 27 and March 14.