Iran has moved political detainees and prisoners from the notorious Evin prison in the capital Tehran, after the complex was hit by deadly Israeli attacks on Monday.
Families of detainees and prisoners have been notified of the inmates' new locations, the semi-official Fars news agency reported, citing the Iran Prisons' Organisation.
Israel claimed it was striking "regime targets" in Monday's attack on the complex. Evin is known to hold political prisoners, dissidents and foreign detainees.
The UN's human rights office condemned the Israeli attack on the prison as a serious violation of international humanitarian law.
"Evin prison is not a military objective, and targeting it constitutes a grave breach of international humanitarian law," UN human rights spokesman Thameen Al Kheetan said in Geneva on Tuesday.
He said the UN had received reports of fires inside the complex and an unspecified number of injuries.
Amnesty International said it was "extremely distressed" by videos showing the damage caused to the jail where hundreds of inmates, including human rights defenders, were being held.
Tuesday's evacuation of Evin came hours after a US-announced ceasefire was supposed to come into effect – but Israel claimed Iran had already breached it. Iran had not officially agreed to the conditions and denied launching missiles towards Israel.
"In light of the severe violation of the ceasefire carried out by the Iranian regime," Israeli Chief of General Staff Eyal Zamir said on Tuesday. "We will respond with force."
Two days after Israel began hostilities on Iran on June 13, prominent Iranian political prisoner Reza Khandan reportedly wrote a letter to the head of the judiciary of Iran, which was published by the Robert F Kennedy Human Rights organisation.
Khandan – accused by the regime of spreading propaganda and colluding to commit crimes against the state – said in the letter that prisoners like him were vulnerable to Israeli strikes.
"As you are well aware, prisons lack air-raid warning systems, shelters, and safe and appropriate evacuation routes to more suitable locations," he wrote.
"Additionally, prisons are not equipped with defence systems to counter potential attacks [especially Ward 8 of Evin, which is in an even worse condition and doesn’t even have a single fire extinguisher]."
Where Khandan is now being held is unknown.
The Israel-Iran conflict has so far killed hundreds of people in Iran and dozens in Israel.
