TEHRAN — Thousands of defiant Iranian opposition supporters, moving in scattered groups in Tehran on Monday, staged what they said was a rally supporting Arab revolts as riot police armed with batons moved in to disperse them, witnesses and opposition websites said.

Iranian authorities blocked access to the house of opposition leader Mir Hossein Mousavi to prevent him from attending the rally which he and fellow opposition leader Mehdi Karroubi had sought to hold.

While Iran has backed the Arab uprisings in Tunisia and Egypt, the interior ministry in Tehran banned the rally saying it was a ploy by the opposition to stage anti-government demonstrations as seen in 2009 after the re-election of President Mahmoud Ahmadinejad.

Witnesses and opposition websites reported that thousands of opposition supporters were walking in scattered crowds silently towards Tehran's prominent Azadi Square (Freedom Square) from several parts of the capital as policemen kept a sharp watch and tried dispersing them.

Riot police on motorbikes armed with shotguns, tear gas, batons, paintball guns and fire extinguishers were deployed in key squares in the capital to prevent the gatherings.

One witness described how one group of demonstrators was walking silently from Imam Hussein Square to Enghelab Square. "They are being silent and trying to keep a low profile," the witness said.

"Some policemen are chasing protesters in order to disperse them," another witness said, adding around 1,000 anti-riot policemen were also deployed in and around Imam Hussein Square.

More police and Basij militiamen took up positions in Haft-e Tir square, a regular site for intense anti-government protests in 2009.

The foreign media has been banned by authorities from on-the-spot reporting of the gatherings.

Police meanwhile stopped Mousavi and his wife Zahra Rahnavard from attending the rally as they tried to step out of their house at around 2:45 pm (1115 GMT), Mousavi's website Kaleme.com reported.

Kaleme.com said earlier that police had blocked access to Mousavi's house since early Monday. "From today the police have blocked the alley where their house is located...There is no possibility of coming and going," it said.

The report said all telephone lines at the house, including the mobile phone connections of Mousavi and his wife, have been severed.

Kaleme.com said the latest "illegal and restrictive measures and pressures were adopted to prevent Mousavi from taking part in a rally in support of the people of Tunisia and Egypt."

Karroubi himself has been under de facto house arrest for almost a week with his family and relatives barred from visiting him.

The cleric's website Sahamnews.org said on Monday that his wife, Fatemeh, was barred also from leaving the house.

The two leaders and their supporters remain steadfast in rejecting Ahmadinejad's presidency, saying the hardliner was re-elected due to massive vote rigging in June 2009.

Their protests in the immediate aftermath of the election brought hundreds of thousands of people on to the streets of Tehran and other cities, shaking the pillars of the Islamic regime and dividing the nation's elite clergy.

Iranian authorities crushed those demonstrations during which scores of people were killed and wounded, and thousands arrested in a crackdown by security forces and members of the feared Basij militia.

Iranian officials, including commanders from the elite military force, the Revolutionary Guards, and the Basij militia have warned the opposition against staging Monday's rally.

Basij commander Mohammad Reza Naghdi on Sunday said Western spies wanted to ignite a revolt in Iran similar to those which raged in Tunisia and Egypt and that they were searching for "a mentally challenged person who could set himself on fire."

Naghdi said his militiamen were "ready to sacrifice their lives" to defend the Islamic regime against an opposition which he likened to the "party of Satan."