By Jim Muir BBC Tehran correspondent

It has been announced that Iran's Supreme Leader Ayatollah Ali Khamenei has agreed to commute the remaining sentence of one of the most prominent reformists jailed for dissidence.

Khamenei commuted Nouri's sentence

Abdullah Nouri - former vice-president and interior minister - has served three years of a five-year sentence, after a special clerical court found him guilty of insulting Islam and the leader of the Islamic revolution, Ayatollah Khomeini.

The pardon came in response to an appeal from the speaker of parliament and a number of MPs, who pointed out that Mr Nouri's brother, Ali Reza - himself a prominent reformist deputy - was killed in a car crash last week.

Meanwhile, it has been reported that another leading figure in the reformist movement, Abbas Abdi, was arrested at his home in the capital, Tehran.

His arrest comes amid a crackdown by the hardline judiciary on organisations conducting public opinion polls.

Poll clampdown

Mr Abdi was director of a polling organisation that was closed down last week.

Abdi's firm polled Iranians about their feelings towards the US

A spokesman for the biggest reform faction, the Participation Front, said that security officials went to Mr Abdi's house mid-morning and searched it, and he was then arrested and taken away.

There was no immediate word from the judiciary as to why it had ordered a detention which is bound to cause a storm in political circles, given Mr Abdi's status as one of the leading lights in the reform movement, although he holds no official post.

But it is widely believed the arrest is in connection with the judiciary's current campaign against polling organisations which have been producing reports not welcomed by the right-wing faction.

Mr Abdi's own outfit, called Ayandeh, was closed down four days ago and another of its directors, Hossein Qazian, detained.

Timeline: US embassy hostage crisis

Nov 79 - Iranian students seize 63 hostages and demand return of Shah to face trial April 80 - Secret US rescue mission ends in disaster in desert with eight marines dead Jan 81 - Last 52 hostages freed after intense negotiation

Ayandeh had conducted a poll on behalf of Gallup late last year on attitudes to the United States.

But the judge in charge of the case has also said that British officials had recently held discussions with Ayandeh about the possibility of conducting a poll on Iranian relations with the UK.

Mr Abdi's arrest came, ironically, as hardliners were commemorating the anniversary of the storming of the American embassy in Tehran by militant students in 1979.

Mr Abdi was one of the leading figures in the embassy takeover, but now, like many of his comrades, he is a prominent advocate of reform at home, and detente with the outside world.

Demonstration

Just as Mr Abdi was being detained, a demonstration was being staged near the former US embassy in central Tehran, which is now a Revolutionary Guards facility.

Several thousand people chanted "Death to America!" and burnt the US and British flags.

Iranians commemorated the takeover of the US embassy

The crowd was smaller than in previous years despite a good deal of mobilisation by the hardline establishment.

Many of those taking part were schoolchildren who had been given the day off and bussed in for the occasion.

Such demonstrations are organised every year, but are not attended by reformists such as Abbas Abdi and others who took part in the embassy seizure, which led to a rupture of relations between the two countries as US diplomats were held hostage for 444 days.

The closure of Ayandeh and the arrest of its directors follows a similar move by the judiciary last month against another company which had conducted a poll on Iranian attitudes to relations with the US.

The results, widely published in the reformist press, said that around three-quarters of those polled favoured negotiations with Washington aimed at restoring normal relations.

Hardliners have accused the pollsters of fabricating the results, and also of selling secrets to foreign powers by conducting a poll commissioned by the Japanese embassy on Iranian public perceptions of Japan.