Four members of the Iranian parliament have started a 48-hour sit-in at the parliament building in Tehran to protest against the recent arrests of student leaders and activists.

The four MPs expressed concern at the way the students were arrested and fear that they might be maltreated during interrogation.

The detentions took place after the wave of night-time street protests that shook the capital and other Iranian cities for 10 days in mid-June.

The four MPs were all elected with the support of the student movement.

They said the students had been arrested by force and, in at least one case, at gunpoint. It was not clear who had detained them, where they were being held, and what charges they faced.

All of this, they said, was out of line with the constitution. If the authorities behave illegally, one of the MPs said, how can we expect ordinary people to abide by the law?

Vigilantes role

One of the MPs argued that instead of arresting students, the powers-that-be should tackle the so-called plainclothes rogue elements - the right-wing Islamic vigilantes who were allowed to attack the demonstrators and beat them savagely with clubs and chains, causing many injuries.

The MPs said the vigilantes were not rogue elements at all, but were organised and controlled.

They called on the reformist President, Mohammad Khatami, to identify who was behind them.

Iran's public prosecutor has said that 4,000 people were arrested during the disturbances around the country, and half of them were still being held.

The four MPs accused the right-wing judiciary of trying to exploit the unrest to dissolve the main student organisation.

Student groups have expressed fears that their arrested colleagues may be subjected to physical and psychological torture in order to extract confessions.

The crackdown is widely seen as an effort to deter any trouble on 9 July - the fourth anniversary of the raid on a Tehran student dormitory by riot police and right-wing vigilantes that triggered several days of violent street disturbances.

The authorities have banned any rallies or meetings to mark the anniversary either on or off campus.