The U.N. human rights office on Friday voiced concern about Iran’s treatment of detained protesters and said that authorities were refusing to release some of the bodies of those killed.

The death of 22-year-old Mahsa Amini in police custody last month has ignited protests in one of the boldest challenges to Iran’s clerical leadership since the 1979 revolution. Rights groups have said at least 250 protesters have been killed and thousands arrested.

“We’ve seen a lot of ill treatment … but also harassment of the families of protesters,” Ravina Shamdasani, spokesperson of the Office of the High Commissioner for Human Rights, told a Geneva press briefing, citing multiple sources.

“Of particular concern is information that authorities have been moving injured protesters from hospitals to detention facilities and refusing to release the bodies of those killed to their families,” she said.

Shamdasani added that in some cases, authorities were placing conditions on the release of bodies, asking families not to hold a funeral or speak to the media. Protesters in detention were also sometimes being denied medical treatment, she said.