The Tehran student protests are the most serious disturbances in Iran since the election of reformist President Mohammad Khatami two years ago.

They come after months of intensifying struggle between Mr Khatami's reform movement and the old guard of religious hard-liners.

Sadeq Saba: Students showing they are still a force to be reckoned with

Iranian students - who played a major role in overthrowing the monarchy in 1979 - have become a powerful force in favour of Mr Khatami's reform programme.

The students who took to the streets this week have broadened their original demands for the lifting of a ban on a pro-Khatami newspaper and protection of press freedom.

Now they are calling for more wide-ranging reforms, presenting an even more radical challenge to the conservative establishment than the president.

Soul of the revolution

With crucial parliamentary elections due in the spring next year, conservatives and reformers are fighting an increasingly bitter battle for the soul of the Iranian revolution.

Scenes outside the university were reminiscent of the 1979 revolution

Mr Khatami has been promoting openness, human rights and democratic reforms. He has also sought to build bridges with countries which once feared and mistrusted the Islamic republic.

In recent months, the hard-liners have targeted press reforms under which an increasingly outspoken free press has emerged.

The student unrest follows new parliamentary legislation to curb press freedom and the banning of a leading pro-Khatami newspaper, Salam.

Press clampdown

Prominent pro-Khatami journalists, including the director of the country's official news agency Irna, Fereydoun Verdinejad, have also been arrested and charged by special courts.

Culture Minister Ataollah Mohajarani, who spearheaded Mr Khatami's press reforms, narrowly avoided impeachment by parliament for "corrupting Islamic values".

Away from the media, key Khatami ally Gholamhossein Karbaschi, Mayor of Tehran, was jailed for corruption charges despite a petition signed by nearly half the country's MPs calling for him to be pardoned.

The moderates, meanwhile, have their eyes on hard-line control of the powerful security and intelligence services.

Beatings and deaths

It was the harsh nature of the security operation against recent student demonstrations, with reports of beatings and even deaths, that has provoked thousands of students to come out onto the streets.

The protesters also say right-wing thugs acting on behalf of the anti-Khatami camp have been conducting attacks and provocations.

And in an unprecedented move, they have directly addressed Iran's supreme leader, Ayatollah Ali Khamenei, calling on him to take responsibility for the actions of the security men.

This radical campus mood appears to have caught Mr Khatami's government by surprise.