U.N. High Commissioner for Human Rights Michelle Bachelet said Friday there is growing evidence of war crimes in Ukraine, with the majority of violations attributable to Russian forces.

The U.N. Human Rights Monitoring Mission in Ukraine has been gathering and documenting evidence of hundreds of alleged unlawful killings of civilians in Bucha, and in towns in the regions of Kyiv, Chernihiv, Kharkiv, and Sumy. All of those places were under the control of Russian armed forces in late February and early March.

Bachelet said Russian armed forces have indiscriminately shelled and bombed populated areas. Her spokeswoman, Ravina Shamdasani, said they killed civilians and wrecked hospitals, schools and other civilian infrastructure, actions that may amount to war crimes.

She said the monitoring mission verified more than 5,260 civilian casualties, including 2,345 killed and 2,919 injured. More than 92 percent of the casualties were recorded in government-controlled territory and the rest in Russian-controlled regions of Donetsk and Luhansk in eastern Ukraine.

“We know that the actual numbers are going to be much higher as the horrors inflicted in these areas of intense fighting, such as Mariupol, come to light,” Shamdasani said. “The scale of summary executions of civilians in areas previously occupied by Russian forces are also emerging. The preservation of evidence and the decent treatment of mortal remains must be ensured, as well as the psychological and other relief for victims and their relatives.”

Shamdasani said the willful killing of protected people, including summary executions, are gross violations of international human rights law and serious violations of international humanitarian law, and amount to war crimes.

The monitoring mission also documented what appears to be the use of cluster munitions by Ukrainian armed forces in the east of the country. Those weapons indiscriminately kill and maim civilians and are banned under international law.