The World Health Organization (WHO) says it has "documented 200 attacks on hospitals and clinics" in Ukraine, adding that it is gathering evidence for a possible investigation into war crimes in the attacks.

"Intentional attacks on healthcare facilities are a violation of international humanitarian law and as such - based on the investigation and attribution of the attack - represent war crimes in any situation," said WHO Director of Emergencies Mike Ryan. on Saturday in the Ukrainian capital Kiev.

"We continue to document and testify about these attacks… and we are confident that the UN system and the International Criminal Court and others will undertake the necessary investigations to assess the criminal intent behind these attacks."

Ryan, in an unannounced visit together with the head of the WHO, Tedros Adhanom Ghebreyesus, said at a press conference that it was the clear responsibility of the warring parties to avoid the attack on health facilities, Telegrafi reports.

Russia has denied previous allegations by Ukraine and Western countries about possible war crimes and has also denied targeting civilians in the war.

Ryan said the 200 cases did not represent the entirety of the attacks on Ukrainian medical facilities, only those that the WHO had verified.

Kiev has said there have been about 400 such attacks since Russia invaded Ukraine on February 24.

"My message to all the people of Ukraine is this: 'The WHO stands by you… We continue to call on the Russian Federation to stop this war,'" Ghebreyesus told a news conference.