TEHRAN - Police deployed in force around Tehran University on Monday, witnesses said, as defiant Iranian students called for mass protests against President Mahmoud Ahmadinejad to mark Students Day.

Ahmadinejad's main rival Mir Hossein Mousavi also challenged the authorities, saying they would be unable to "quell" the expected protests which the foreign media has been banned from reporting.

"We are asking all people to come to universities so we can have one voice to protest at the coup d'etat," said an online statement posted by students of the prestigious Amir Kabir University, who called themselves the "green university students of Iranian universities."

Green was the signature colour of Mousavi's election campaign for the June 12 presidential poll. He lost to Ahmadinejad in what he claims was a "fraudulent" election staged to return the hardliner to power.

Since then his supporters have taken to streets in Tehran at the slightest opportunity to demonstrate against Ahmadinejad, accusing him of "stealing their votes."

Hundreds of thousands of protesters poured onto streets in the immediate aftermath of the poll and in the deadly unrest that followed dozens were killed and thousands arrested.

The defiant protests shook the pillars of the Iranian regime in what was one of its worst crises since the 1979 Islamic revolution.

Around 140 top reformists, political activists, and journalists have also been brought to court in what opposition leaders claim to be "show trials."

Several websites have reported that Iranian opposition groups are planning to use Monday's regime-sponsored event to stage fresh protests against Ahmadinejad.

Every year on December 7, Tehran campuses mark the 1953 killing by the shah's security forces of three students, just months after a US-backed coup toppled popular prime minister Mohammad Mossadeq.

The elite Revolutionary Guards and other authorities have warned they will crack down on any attempt by regime opponents to hijack the event.

The statement by the Amir Kabir university students said their "programme will start at 12:00 (0830 GMT) and we are asking civil servants, students, housewives and great men Mousavi and (Mehdi) Karroubi to participate from 3:00 pm (1130 GMT)."

Anticipating mass protests, hundreds of police have been deployed around Tehran University, one of the city's most politically sensitive institutions, to prevent the protests, witnesses told AFP.

"Police have also cordoned off side lanes going towards Tehran university," a witness said.

Neither Mousavi nor Karroubi have issued direct calls for protests on Monday, but the former has challenged the authorities as they moved to prevent them.

"If you silence all the universities, what can you do with the situation of the society?" Mousavi asked in a statement posted on his website Kaleme.com.

He warned Iranian authorities they are "fighting with shadows in the streets," referring to protesters.

"If you quell the 16th of Azar (Monday), what will you do on the 17th or the 18th?" he said, indicating that protests would continue to take place.

The conservative bloc of Iran's parliament, meanwhile, urged opposition figures to give up their "political obstinacy."

"... we have ample proof the reformists wanted to substitute the Islamic regime with a secular democracy" after the election, the official IRNA news agency quoted the statement as saying.

"We have only one expectation from those who have long history in the Islamic revolution which is to follow the path of Velayat e-Faqi in order to make Americans and their lackeys desperate," it said, referring to the doctrine of Iranian revolutionary leader Ayatollah Ruhollah Khomeini.

"So we recommend to the gentlemen (opposition figures) to give up their behaviour which smells of political obstinacy."

Aside from banning the foreign media from covering Monday's events, the authorities have also cut Internet connections and blocked access to several opposition websites.