A revolutionary guerrilla group inside Iran, the Babak Khorramindin Organisation (BKO), claimed responsibility for the blast, but the Iranian news agency, Irna, quoted the head of prisons as saying that a short-circuit had led to a fire setting off mines near the prison wall.
Yesterday reports reached the West of violent demonstrations last week in Najaf-Abad, near Isfahan, between the Law and Order Forces and local people. Despite an official news blackout, the reports said that more than 100 people had been killed in the fighting and more than 1,000 arrested.
The demonstrations in Najaf-Abad started last week after the regime imprisoned the new Friday imam of the city, Hojatoleslam Izadi, a follower of the dissident Grand Ayatollah Hosseinali Montazeri, who is under house arrest in Qom.
Informed religious sources said that five men who were hanged last Wednesday in Qom were pro-Montazeri mullahs, who had protested against the blood-letting in Najaf-Abad.
The Evin prison became notorious during the rule of the late Shah of Iran as a place where political prisoners were held. It continued to be used by the government after the 1979 Islamic revolution.
The BKO guerrillas said that the blast at the prison had been carried out as a reprisal for the bombing of the Imam Reza Shrine in the north-eastern city of Mashad on 20 June in which 26 people died.
The government has said that the attack on the shrine, the murder of two Christian ministers and several foiled bombings are all part of a campaign directed by the Iraqi- based opposition group, the Mujahedin Khalq.
'Murders, explosions, killing of senior Christian clerics were to be blamed on the people or the government or Sunnis or Shias, so that people would say sectarian conflicts are aggravated,' said Ayatollah Mohammad Yazdi, Iran's most senior judge.