By Jim Muir BBC correspondent in Tehran

A series of violent night-time disturbances in the Iranian capital Tehran and in other cities over the past 10 days appears to have largely died away, but has left a tense political fallout.

Student protests have now spread to other parts of the population

The nocturnal clashes, initially focused on Tehran University, spread to the streets and led to hundreds of arrests.

Many pro-reform protesters were injured in attacks by right-wing vigilantes.

Incidents have continued nightly in the suburb of Tehran Pars, on the eastern edge of the capital.

Witnesses said several protesters were badly hurt there on Friday night, including one woman who received near-fatal stab wounds while several other women were clubbed around the head.

Those responsible are believed to be basijis and hezbollahis, right-wing Islamic irregulars, often teenagers, who roam around trouble-spots on motorcycles armed with clubs, chains, and knives, apparently acting with impunity.

The activities of these vigilantes was denounced in a statement signed by 166 reformist deputies (a majority of the 290-member parliament) which was read out on Tehran radio on Sunday.

The statement blamed these "violent and ruthless plain-clothes rogue elements" as the main factor provoking the disturbances. It called for them to be put on trial and punished.

The parliamentary statement also condemned what it called "efforts by known circles to exploit the current situation" to discredit the reformist student movement and other political groups by linking them to the unrest.

Stifling dissent

Scores of student activists and some liberal political figures are reported to have been arrested in recent days in Tehran and around the country.

The detentions took place on direct orders from the hard-line judiciary, bypassing normal procedures, with plain-clothes court agents apparently being given a blank cheque to arrest anybody they deemed "suspicious".

Students in Tehran talk about their protest In pictures

It is widely seen as an attempt to stifle dissent in advance of 9 July, the fourth anniversary of serious riots which broke out in Tehran after police and vigilantes attacked a student dormitory.

The anniversary was expected to be a focal point for protests against the regime.

In the 10 days of disturbances in the capital, police chiefs say more than 500 people were arrested.

Almost all of them were aged between 17 and 25, but only 10 of them were students, according to Brigadier Mahmood Japloghi, police commander of Tehran province.

Many other people were reported detained after similar disturbances in other cities in different parts of the country.

Widespread dismay

The fact that so few students were reported among those arrested during the clashes indicated that the dissent was by no means confined to the campuses where the trouble began.

Many of those taking part in the protests, which later took the form of horn-sounding in traffic jams, were ordinary people, often families, who wanted to register their dismay that so little of the change they have been voting for since 1997 has been brought about.

But the unrest has also been openly incited by TV and radio stations and websites run largely from the US by Iranian exiles bitterly opposed to the Islamic regime.

The stations broadcast their message in Farsi directly into Iran, and are widely followed.

Police have tried to regain control of Tehran's streets

This, and encouragement for the protesters voiced by American officials from President Bush down, has allowed the regime's hard-liners to dismiss the demonstrators as hooligans and traitors dancing to Washington's tune.

The extreme hard-line former head of the judiciary, Ayatollah Mohammad Yazdi, called on the courts to treat those arrested as moharebs, people making war on God - a charge carrying an automatic death penalty.

The Public Prosecutor, Ayatollah Abd an-Nabi Namazi, said that "those who spread insecurity in society" would be handled "with repressive force".

The scale of the crackdown and the wave of arrests gave rise to a widely circulated conspiracy theory suggesting that regime loyalists fomented the unrest in order to justify taking steps to defuse possible trouble in advance of the 9 July anniversary.

Unorganised opposition

Few analysts believe that at current levels the unrest amounts to a serious threat to the regime.

The authorities deployed only a fraction of their potential defence mechanisms against demonstrations which never involved more than a few thousand people.

Islamic vigilantes may be responsible for some of the violence

While disaffection is undoubtedly widespread because of the failure of massively elected reformists to make much difference, opposition is vague and unorganised.

There is no political vehicle or unifying ideology to channel dissent.

Since the 1999 riots - which, like the recent disturbances, spilled from the campuses onto the streets - the main student organisation has been split and many of its more militant leaders arrested or otherwise curbed.

Liberal but peaceful opposition groups outside the Islamic system, such as the Freedom Movement of Iran and related "religious nationalist" elements, have been severely pressured.

Peaceful change

The regime's hard-core outright opponents are based abroad because they would be ruthlessly suppressed inside the country.

The most vocal of these, the People's Mujahideen or Mujahidin-e-Khalq, is an effective propaganda voice abroad and used to mount pinprick military operations from Iraq.

But it has negligible support among Iranians inside the country because it allied itself with Saddam Hussein's Baghdad and is seen by many as ideologically less desirable even than the current Islamic system.

Royalists, grouped behind Reza Pahlavi, the son of the late deposed shah, also enjoy little support among the bulk of the people, to whom the monarchy appears an irrelevance.

Having experienced a turbulent revolution and eight years of war (with neighbouring Iraq) in the past 25 years, few Iranians advocate violent anti-regime upheavals because they know that would take their dreams of a better life even further beyond their grasp.

Hence the massive vote they gave to the idea of gradual, peaceful change from within the system.

First steps

But President Mohammad Khatami and the reformist MPs who now dominate parliament have been unable to break the grip on real power of the entrenched hard-line minority, leading to widespread public disillusion.

President Khatami is fighting an uphill battle to reform Iran

The resulting frustration has undoubtedly created a tense and unpredictable situation.

But peaceful dissent would have to be on a much more massive scale, involving millions rather than thousands, if it were to have a serious impact on the regime.

The latest unrest may not have gone completely without impact, however.

The violent behaviour of the Islamic vigilantes has increased pressure within the regime to bring the imposition of law and order more strictly under the control of official law enforcement forces, and some first steps have been taken in that direction.