The men were convicted of involvement in a bombing spree after secret trials. But activists insist they are innocent and paying the price for merely hailing from the country's downtrodden Arab minority.

It is feared they could be hanged as early as today because their 'confessions' were broadcast on Iranian television on Monday night.

Two other ethnic Arabs were publicly hanged from a crane in March just two days after their heavily-edited 'confessions' were televised.

Public executions are not uncommon in the Islamic Republic. It carries out more every year than any country but China. Some are particularly gruesome.

In front of a baying crowd last year, serial child killer Mohammad Bijeh was flogged at the stake, stabbed in the back by the 17-year-old brother of one of his 16 victims and stoned by the chanting mob.

Then, to shouts of 'make him twist', he was hoisted up on a crane by a noose that had been placed around his neck by the mother of another victim.

It took more than five minutes for him to choke to death while he was taunted and spat at. 'Dance and think of what you did to our kids,' one bereaved father shouted. His corpse was then left dangling for another 20 minutes.

The 11 were convicted for their alleged role in explosions that killed more than 20 people in Iran's oil-rich province of Khuzestan last year.

The slow strangulation method to be used on them is designed to maximise suffering. It prolongs the agony and 'intimidates the public', said Dr Karim Abdian, executive director of the Ahwaz Human Rights Organisation in Washington.

The 11 were due to be hanged in the city of Ahwaz, capital of Khuzestan, where ethnic Arabs are a majority.

Now it is believed the hangings will take place in several cities with largely Arab populations to spread the fear, said Dr Abdian.

The imminent executions are raising a storm of protest from British MPs. Human rights campaigner Peter Tatchell, backed by Labour MP Chris Bryant and Tory MP Michael Gove, is urging the Government to petition Iran to commute the executions. 'The men were tortured into giving false confessions,' said Mr Tatchell.

The sentences were imposed after trials behind closed doors which human rights groups say did not meet international standards. One of the condemned men was even in jail at the time of the bombings.

Iranian and foreign activists say the trials of the 11 were flawed, the charges baseless and the sentencing based on a spurious interpretation of the law.

'We've challenged the regime if they have any evidence whatsoever of any crime to show it and they haven't been able to show a shred of evidence,' said Dr Abdian.

The condemned men come from three groups, he added. Most are from a reformist ethnic Arab party whose goal is to win rights for Ahwazi Arabs through legal and constitutional means.

The peaceful group was banned last week after the Iranian judiciary accused it of inciting unrest and opposing the Islamic system.

Some are human rights activists and others 'are just professionals like engineers and doctors who have been picked just because they are smart people of the Arabs'.