A report by the Organization for Security and Cooperation in Europe (OSCE) said Russia has been violating humanitarian law in Ukraine.
The report said if Russia had respected its international obligations after invading Ukraine on Feb. 24, "the number of civilians killed or injured would have remained much lower."
The 110-page report presented at the OSCE's permanent council meeting pointed at damaged and destroyed houses, hospitals, schools, water stations and other infrastructure.
The three experts who wrote the report, which included information from NGOs on the ground, said given the timeline and scope of their mission it was not possible to identify war crimes.
"Nevertheless, the mission found clear patterns of international humanitarian law violations by the Russian forces in their conduct of hostilities," the report said.
The mission was set up following a request by Ukraine on March 3.
It covers the period from the invasion on Feb. 24 to April 1, before images of bodies emerged as Russia withdrew from the town of Bucha and elsewhere in northern Ukraine.
The images shocked the world and prompted accusations of Russian war crimes.
The report noted that "evidence points to a major war crime and a crime against humanity committed by the Russian forces," calling for an international probe.
The report's authors said it was "likely" other "violent acts" documented, such as targeted killing, enforced disappearance or abductions of civilians, qualified as a crime against humanity.
The report also found the conflict "has exerted and continues to exert particularly negative effects" on women, children, older people and people with disabilities.
It also expressed "concern" over Ukraine's treatment of prisoners.
"As this report shows, violations occurred on the Ukrainian as well as on the Russian side. The violations committed by the Russian Federation, however, are by far larger in scale and nature," it said.
The report was carried out under the OSCE's so-called Moscow Mechanism, which allows for an ad hoc team of experts to be established to assist in resolving an OSCE member state's problems.
Russia declined to contribute to the report, according to the experts, deeming the mechanism "largely outdated and redundant."
The OSCE began in the early 1970s as a forum for dialogue between East and West.
The Vienna-based body has 57 member states on three continents – including Russia, Ukraine and the United States.
