Experts as part of a UN fact-finding mission will travel to Donbas in the coming days to investigate the shelling of a pretrial detention facility in Olenivka, UN Under-Secretary-General Rosemary DiCarlo has said on Wednesday.

"The Fact-Finding mission to Olenivka is set to deploy in the coming days to look into the incident on 29 July that led to the death of 53 Ukrainian prisoners of war. Between 75 and 130 more were injured," she said.

"The head of the mission, Lieutenant General Carlos Alberto dos Santos Cruz, is accompanied by an experienced team of senior officials and experts. The mission must be able to conduct its work without any interference and have safe, secure and unfettered access to people, places and evidence," she said.