The Iranian regime has appointed one of its most feared prosecutors to interrogate reformists arrested during demonstrations, prompting fears of a brutal crackdown against dissent.

Relatives of several detained protesters have confirmed that the interrogation of prisoners is now being headed by Saaed Mortazavi, a figure known in Iran as “the butcher of the press”. He gained notoriety for his role in the death of a Canadian-Iranian photographer who was tortured, beaten and raped during her detention in 2003.

“The leading role of Saeed Mortazavi in the crackdown in Tehran should set off alarm bells for anyone familiar with his record,” said Sarah Leah Whitson, the Middle East and North Africa director of Human Rights Watch.

As prosecutor-general of Tehran since 2003 and as a judge before that, he ordered the closure of more than 100 newspapers, journals and websites deemed hostile to the Establishment. In 2004 he was behind the detention of more than 20 bloggers and journalists, who were held for long periods of solitary confinement in secret prisons, where they were allegedly coerced into signing false confessions.

Mr Mortazavi has also led a crackdown in Tehran that has seen women arrested for wearing supposedly immodest clothing.

Earlier this year he oversaw the arrest and trial of Roxana Saberi, the American-Iranian journalist sentenced to eight years for spying, and his name has appeared on the arrest warrants of prominent reformists rounded up since the unrest started, such as Saeed Hajarian, a close aide of Mohammad Khatami, the reformist former President. With more than 600 people now having been arrested, including dozens of journalists, many fear the worst.

Mr Mortazavi became notorious for his role in the death of Zahra Kazemi while in Iranian custody on July 11, 2003. Kazemi, a freelance photojournalist with dual Iranian-Canadian nationality, was arrested while taking photographs outside Evin prison, Tehran, during an earlier period of reformist unrest in the city, also ruthlessly repressed.

The first news of what happened to Kazemi, 54, came in a statement from Mr Mortazavi, which said that she had died accidentally of a stroke while being interrogated.

Two days later a contradictory statement was issued, saying that she had fallen and hit her head.

On July 16 Mohammad Ali Abtahi, the Vice-President, admitted that Kazemi had died of a fractured skull after being beaten.

Mr Abtahi, who is no longer in office, was also arrested in the round-up of hundreds of dissidents and reformists overseen by Mr Mortazavi last week.

On July 21, Mr Mortazavi was appointed to head the official investigation into Kazemi's death. Reformists protested, saying that he lacked independence as he was involved in the case, and that as prosecutor general it had been his duty to ensure Kazemi's well-being in custody. The appointment went ahead anyway.

Shirin Ebadi, the Nobel prize-winning lawyer who represented Kazemi's family at the subsequent trial of a junior intelligence officer in July 2004, tried to sub-poena Mr Mortazavi to give evidence, but the judge declined. The defendant was cleared of the charge of semi-intentional murder.

There the matter rested until March 2005, when Shahram Azam, an Iranian military doctor, claimed asylum in Canada and revealed that he had examined Kazemi's body after her death. He said he had seen obvious signs of torture, including a fractured skull, broken nose, crushed toe, missing fingernails, broken fingers, marks from flogging, deep scratches on her neck, and severe abdominal bruising. A female nurse who examined Kazemi's genitals - he said he was forbidden to do so as a male doctor - told him there were signs of brutal rape.

Dr Azam's evidence reignited concern at Kazemi's death, with blame coalescing around Mr Mortazavi. The Canadian government continues to maintain that Mr Mortazavi not only ordered Kazemi's arrest but supervised her torture and was present when she was killed.

Reporters without Borders concurs: "It was Mortazavi who was chiefly responsible for Canadian-Iranian press photographer Zahra Kazemi's death."

Mr Mortazavi has repeatedly been accused of human rights abuses in the treatment of other detainees, including journalists who said they received death threats after reporting their alleged torture on Mr Mortazavi's orders while in custody in 2005, and students who say they were mistreated after they were pre-emptively arrested in 2008 because they were suspected of planning protests.

It was seen as a black joke when, in 2006, Iran selected Mr Mortazavi to lead its delegation to a meeting of the the United Nations Human Rights Council. Human Rights Watch appealed unsuccessfully for him to be dropped from the delegation, or for other nations to refuse to meet the Iran delegation while he remained in it.

Mr Mortazavi used his right to address the council to give a speech arguing that all nations had the right to free access to nuclear power, and accusing the council of being a catspaw of Western powers. He urged it to turn its attention to human rights abuses by the West, including bans on Holocaust denial, hostility to the burka, and atrocities committed by America during its War on Terror.

Times Recommends

• Would you live on the wrong side of the Berlin Wall?
• Wish you were here, says Iraq tourist board
• Russian policeman’s corruption plea to Putin