Many executions have been carried out in public in an apparent bid to create a climate of intimidation while sending out uncompromising signals to the West. Opposition sources say at least three of the dead were political activists, contradicting government insistence that it is targeting 'thugs' and dangerous criminals. The executions have coincided with a crackdown on student activists and academics accused of trying to foment a 'soft revolution' with US support.

The most high-profile recent executions involved Majid Kavousifar, 28, and his nephew, Hossein Kavousifar, 24, hanged for the murder of a hardline judge, Hassan Moghaddas, a man notorious for jailing political dissidents. They were hanged from cranes and hoisted high above one of Tehran's busiest thoroughfares.

The spectacle, the first public executions in Tehran for five years, took place outside the judiciary department headquarters where Moghaddas was murdered. But the location, near many office blocks and the Australian and Japanese embassies, meant they were seen by many middle-class Iranians who would not normally witness such events.

The previous day seven men were publicly executed in the north-eastern city of Masshad, including five said to be guilty of 'rape, kidnapping, theft and committing indecent acts'. Another two were hanged separately for raping and robbing a young woman. The executions were also shown live on state television.

Public hangings are normally carried out sparingly in Iran and reserved for cases that have provoked public outrage, such as serial murders or child killings. Human rights organisations say the rising death toll has brought the number of prisoners executed this year to about 150, compared to 177 in 2006, a dramatic increase in capital punishment since the country's radical President, Mahmoud Ahmadinejad, took office two years ago.

The executions come after the government launched a campaign targeting murderers, sex offenders, drug traffickers and others cast as a threat to 'social security'. It resulted in a wave of arrests after police raided working-class neighbourhoods in Tehran and other cities. Those arrested were paraded in public, often in humiliating poses.

The government has also sought to publicise executions conducted behind closed doors. Last month state television broadcast footage of 12 condemned men as they were about to be hanged in Tehran's Evin prison. The authorities said they had been guilty of 'rape, sodomy and assault and battery'. Opposition sources say at least three were political activists, though they have not disclosed their identities. Asiran, a government website, dismissed the claims as 'lies'.

International gay rights campaigners have also said that homosexual men were among the executed. Homosexuality is a capital offence in Iran, along with adultery, espionage, armed robbery, drug trafficking and apostasy.

Iran has long been one of the world's most prolific exponents of the death penalty and ranks second only to China in the number of executions. Human rights groups say it has the world's worst record for executions for crimes committed when the defendant was under 18.

However, there have been signs of official disquiet over the recent trend. Ayatollah Mahmoud Hashemi Shahroudi, the relatively moderate judiciary chief, has made an apparent protest by openly criticising Ahmadinejad's government on a range of issues. He also signalled displeasure with the repressive climate by ordering officials to investigate claims that student activists were tortured during a recent detention in Evin prison.

Shahroudi is believed to have been unhappy over the stoning to death last month of a man convicted of adultery after he had ordered a stay of execution.

However, the spate of executions seems likely to continue. Tehran's hardline chief prosecutor, Saeed Mortazavi, has announced that he is seeking the death penalty against 17 'hooligans'.