Sporadic clashes erupted in Tehran yesterday between security forces and anti-government protesters, witnesses reported.
The demonstrators chanted "death to the dictator," referring to Iran's hardline president, Mahmoud Ahmadinejad, who the opposition believes was re-elected through fraud in 2009.
Witnesses and opposition websites reported that thousands of opposition supporters were walking silently in scattered groups towards Tehran's Azadi Square (Freedom Square) as policemen kept watch and tried dispersing them. Police on motorbikes armed with shotguns, tear gas, batons, paintball guns and fire extinguishers were deployed in major squares.
Iran's opposition called for yesterday's demonstration to march in support of Egypt's protest that forced the president, Hosni Mubarak, to resign. While Iran has backed the Egyptian uprising, the interior ministry banned the Tehran rally, saying it was a ploy by the opposition to stage anti-government demonstrations, as seen in 2009 after the re-election of Mr Ahmadinejad.
Iranian authorities blocked the access of the opposition leader, Mir Hossein Mousavi, to the rally which he, and the fellow opposition leader, Mehdi Karroubi, had sought to hold.
Opposition leaders had requested permission earlier to stage the rally but the government rejected the request.
An interior ministry deputy, Mehdi Sadr Alikhani, on Sunday said that the ministry was not going to allow "seditionists" take to the streets. But an adviser to Mr Karroubi, Esmail Germai Moqadam, told the BBC Persian television that, based on the Iranian Constitution, no permission was required.
Ardashir Amir Arjomand, an adviser to Mr Mousavi, told the BBC Persian television on Sunday the same thing. Iranian authorities, he said, "are obliged by the constitution to take all the required measures so that people can express their views in peace and security".
One witness yesterday described how one group of demonstrators was walking quietly 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 that about 1,000 anti-riot policemen were deployed in and around Imam Hussein Square.
More police and Basij militiamen took up positions in Haft-e Tir square, a regular site for anti-government protests in 2009.
Authorities have banned foreign media from reporting at the scenes of the gatherings.
Police meanwhile stopped Mr Mousavi and his wife Zahra Rahnavard from attending the rally as they tried to step out of their house at about 2.45pm local time, Mr Mousavi's website, Kaleme.com, reported.
The website reported earlier that police had blocked access to Mr Mousavi's house since Monday. It said all telephone lines at the house, including the mobile phone connections of Mr Mousavi and his wife, had been severed.
The website 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."
Mr Karroubi 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 yesterday that Mr Karroubi's wife, Fatemeh, was also barred from leaving the house.
Opposition websites reported yesterday that huge crowd had gathered in Tehran after a girl climbed a tower crane and was chanting Green Movement slogans. Videos posted on YouTube showed police trying to bring her down from the crane.
Opposition leaders and their supporters remain steadfast in rejecting Mr Ahmadinejad's presidency, saying his re-election in 2009 was rigged.
By yesterday morning, a Facebook page dedicated to the rally had more than 55,000 followers. Many young people have been using Facebook to invite friends to join their cause.
* With additional reporting by Agence France-Presse and Associated Press