Iranian security forces have arrested about 4,000 people following this month's anti-government protests, first official figures say.

The Prosecutor General, Ayatollah Abdolnabi Namazi, said 40% of those arrested were immediately freed.

"Currently there are 2,000 people who are still in prison, among whom there are not many students," he was quoted as saying.

The protests began on 10 June and led to severe clashes between students and vigilantes loyal to Iran's Supreme leader Ayatollah Ali Khamenei.

In the capital Tehran - the focus of the unrest - 800 people were arrested.

They include Abdullah Momeni and Mahdi Aminzadeh, leaders of the biggest student organisation, the Unity Consolidation Office.

More than a week after he was pulled out of his car and taken away by four plainclothes operatives who sprayed him in the face with a disabling spray, Mr Aminzadeh's family still do not know where he is being held or what charges he faces.

'Policy of repression'

BBC Tehran correspondent Jim Muir said the student leaders had not taken part in the street protests and their arrests have caused outrage in student circles.

As well as criticising the conservative clerics, demonstrators also attacked the reformist President, Mohammad Khatami, who was accused of betraying hopes for change.

And more than 100 student activists havbe now written an open letter to the president asking him to intervene to stop what they called "the policy of repression" which, they said, his continued presence in office would legitimise.

The students, who supported the reform movement and helped vote in Mr Khatami and the reformist majority of the parliament, have warned that they will be alienated from the system if their plight is ignored.

Student associations had vowed to continue to demonstrate until 9 July - the fourth anniversary of the storming of a Tehran University dormitory by police and right-wing vigilantes which set off several days of serious street riots.

The student movement wanted to hold a rally to mark the occasion, but it has been told that no such gatherings will be permitted.

The Iranian protests attracted much support from liberal circles in Iran - as well as from US President George W Bush and UK Prime Minister Tony Blair.

But reformist members of the Iranian establishment joined the conservatives in strongly condemning the US and UK support for the demonstrations.