Iran's police chief admitted yesterday that protesters who were arrested after June's disputed presidential election had been tortured while in custody in a prison in south-west Tehran. But he denied that any of the detainees had died as a result.

General Ismail Ahmadi Moghaddam said the head of the Kahrizak detention centre had been dismissed and jailed. "Three policemen who beat detainees have been jailed as well," the official IRNA news agency quoted Moghaddam as saying.

Human rights groups had previously identified at least three detainees they said had died after torture at Kahrizak, which was closed last month on the orders of Iran's supreme leader, Ayatollah Ali Khamenei. Moghaddam denied that the abuses were responsible for any fatalities there, claiming that an unspecified "viral illness" had caused the deaths.

His admission marked the second occasion in as many days that a senior official had accepted that some criticisms levelled at the regime were well-founded, suggesting growing doubts and uncertainty within the embattled regime.

On Saturday, Qorbanali Dori-Najafabadi, Iran's prosecutor-general, conceded that "mistakes" had led to "painful accidents which cannot be defended, and those who were involved should be punished". He said the mistakes included "the Kahrizak incident", an apparent reference to the deaths.

Dori-Najafabadi indicated that the judiciary had taken overall charge of the detainees and their trials away from the militia and revolutionary guards. He said about 200 people were still being held and urged people not to be afraid to come forward. "Maybe there were cases of torture in the early days after the election, but we are willing to follow up any complaints or irregularities that have taken place," he was quoted as saying.

One of those to die after being detained in Kahrizak was the son of a top adviser to the defeated conservative presidential candidate Mohsen Rezaie. After Mohsen Ruholamini's death, Iran's most senior judge, Ayatollah Mahmoud Hashemi-Shahroudi, ordered officials to inspect all prisons and detention centres. A parliamentary investigation into Kahrizak is also under way.

There have been widespread opposition claims of torture and abuse of the hundreds of anti-government demonstrators, politicians, journalists and academics arrested since Mahmoud Ahmadinejad was declared the winner of the June election.

The result, swiftly endorsed by Khamenei, led to large-scale demonstrations and violent clashes in Tehran and other cities, resulting in dozens, possibly hundreds of deaths and mass arrests. Sporadic protests were continuing despite a harsh security crackdown.Until now, officials had rejected the torture claims.

The website of one of the defeated presidential candidates, Mehdi Karoubi, said yesterday that some of those detained had been raped in detention.

"Some senior officials told me that ... really shameful issues ... Some young male detainees were raped ... also some young female detainees were raped in a way that have caused serious injuries," the website quoted a 10-day-old letter from Karoubi as saying .

Despite Dori-Najafabadi's assurances, Iranian websites reported that relatives and supporters who gathered outside a court in Tehran during the latest trial on Saturday were attacked by riot police when they began chanting slogans.

Saturday's proceedings, condemned as a "show trial" by opposition factions, involved more than 100 people accused of trying to overthrow the Islamic republic. Among those in the dock was Clotilde Reiss, a French researcher working at Isfahan University, who was alleged to have passed information about the protests to the French embassy in Tehran.

Also among the accused was an Iranian citizen, Hossein Rassam, who is employed as a political analyst at the British embassy and who helped to monitor the elections. Both Reiss and Rassam expressed "regret" at their actions, according to the official Fars news agency, and asked for a pardon. Britain and France expressed outrage at the proceedings.