Tehran had not witnessed such scenes since the early years of the Islamic revolution a generation ago.

Rioting students pelting security forces with stones, and setting fire to pictures of the country's Supreme Leader. Running battles with the police in the streets and squares of the city centre, leaving an aftermath of burned-out buses and smashed shopfronts.

The final repercussions and implications of the upheaval will take time to emerge.

But the immediate assessment has to be that the disturbances represent a serious setback - if not a disaster - for Iran's still hugely popular reformist President, Muhammad Khatami, and the civil society movement he heads.

Pressure for change

Protests could destabilise President Khatami's reforms

At first, the crisis seemed destined to be yet another instance of the hard-liners trying to deal a blow to the reformists, only to have it backfire badly on themselves.

The storming of a university dormitory on the night of Thursday 8 July by riot police and right-wing vigilantes - probably from the ultra hard-line Ansar Hizbollah faction - caused an almost universal outcry.

Spontaneous student protests at the destruction, casualties and detentions resulting from the dormitory raid gave the moderate camp another cause celebre with which to press for change.

Student leaders not only demanded the dismissal of the country's hard-line police chief, General Hedayat Lutfian, but also insisted that control of the law enforcement forces should be transferred to the Interior Ministry.

That would bring them under the direct control of President Khatami's reformist government.

Clerical politics

At present, the strings are pulled by the office of the Supreme Leader, Ayatollah Ali Khamenei, who is usually identified with the right-wing conservative camp in Iran's clerical politics.

Such was the strength of outrage over the dormitory incident that even Ayatollah Khamenei was obliged to deplore it and support decisions of the Supreme National Security Council - headed by Mr Khatami - to investigate and punish those involved.

The council announced that two senior police officers were being dismissed and prosecuted, and that the "pressure groups" - right-wing vigilantes - would be firmly curbed.

The crisis seemed destined to yield major benefits for President Khatami and the reformists.

But when riots ended up spilling into the streets, without the support of the mainly pro-Khatami student leaderships, the situation turned around dramatically.

Licence to act

The same combination of riot police, plainclothes security men and right-wing vigilantes who had been condemned for the dormitory raid, suddenly found themselves with a licence to wade in against the rioters on the streets.

Rioting forced the closure of city businesses

Many were beaten up and arrested, but this time there was no outrage because the street violence could not be justified, excused or defended by anyone.

The identity of those involved was also obscure - most student leaders distanced themselves from it - thus enabling the unrest to be labeled as the work of foreign-inspired provocateurs and counter-revolutionaries.

Just as Ayatollah Khamenei had been obliged to condemn the dormitory incident, President Khatami had no choice but to denounce the riots, which caused the city's bazaar to pull down its shutters for the first time since the disturbances began. "They (the riots) were against the interest of the nation, and against the policies of the government. This event is just the opposite of the political development advocated by the government."

Right-wing backlash

The riots have played into the hands of right-wing clerics

Well might Mr Khatami be distressed: The riots played into the hands of the hard-liners, justifying a right-wing backlash which began by bringing the forces of social control to the fore.

Ayatollah Khamenei announced that ''officials in the government, especially those in charge of public security, have been emphatically instructed to put down the corrupt and warring elements with insight and power and, no doubt, those who have invested hope in the mischievous acts of these disgraced elements will be disappointed.

"My basiji children in particular should maintain their full alertness and through their presence everywhere they are needed, terrify and crush the wicked enemies."

The Basij are irregular volunteers attached to the Revolutionary Guards as guardians of the revolution.

There are other reasons why the riots played strongly to Mr Khatami's disadvantage:

• He has always stressed the absolute need for legality, and that his reform programme can only proceed in an atmosphere of calm. Over the past two years, hard-liners have often stirred up trouble of one sort or another precisely to obstruct that process.
• His conservative rivals could blame his liberal ideas for inflaming the young rioters, who chanted slogans supporting Mr Khatami and his reforms.
• The original demands of the students, such as the transfer of control of the police to Mr Khatami's government, are still on the table but have been overtaken by the furore over the street riots.

However, 20 million Iranians voted for him in 1997 hoping for peaceful change.