The UN human rights office on Friday voiced concern at Iran’s treatment of detained protesters and said authorities were refusing to release some of the bodies of those killed, as demonstrators again called for the death of the country’s top leader.

The Islamic Republic has been gripped by demonstrations since the death of 22-year-old Kurdish woman Mahsa Amini in police custody last month. The unrest has posed one of the boldest challenges to Iran’s clerical leadership since the 1979 revolution.

Video footage on social media showed protesters in the city of Zahedan, close to Iran’s southeastern border with Pakistan and Afghanistan, on Friday calling for the death of “dictator” Supreme Leader Ayatollah Ali Khamenei and the Basij militia, which has played a major role in the crackdown on demonstrations.

Dozens of people were killed in clashes in Zahedan four weeks ago during anti-government protests. The provincial security council has said armed dissidents had provoked the clashes, leading to innocent people’s deaths, but admitted “shortcomings” by police.

Rights groups have said at least 250 protesters have been killed and thousands arrested across the country. A tough crackdown by security forces including the feared Basij militia, which has a track record of crushing dissent, has failed to ease the unrest.

“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.

Iran’s Revolutionary Guards said its intelligence unit had foiled a bomb attack in the southern city of Shiraz, two days after a deadly shooting at a shrine there, the guards’ news agency Sepah News said.

Wednesday’s shooting, which was claimed by Daesh, killed 15 worshippers at the Shah Cheragh shrine.