Iranian authorities have poured police and militiamen onto the streets of Tehran to challenge any pro-Egypt marches, which officials worry could turn into demonstrations against Iran's ruling system.
The security clampdown is reminiscent of the backlash that crushed a wave of protests after the disputed re-election of Mahmoud Ahmadinejad in June 2009. But opposition supporters revived a tactic from the unrest, shouting "Allahu Akbar," or God is Great, from rooftops and balconies into the early hours Monday in a sign of defiance toward Iran's leadership.
The reformist website kaleme.com said police stationed several cars in front of the home of Mir Hossein Mousavi ahead of the demonstration called for Monday in central Tehran.
Mousavi and fellow opposition leader Mahdi Karroubi have been under house arrest since last week after they asked the government for permission to hold a rally on Feb. 14 in support of the uprisings in Egypt and Tunisia.
The government rejected the request and warned of repercussions if demonstrations take place.
On Sunday, the opposition renewed its call to supporters to rally, and accused the government of hypocrisy by voicing support for the Egyptian and Tunisian uprisings while refusing to allow Iranian political activists to stage a peaceful demonstration.
"These elements are fully aware of the illegality of their demand and know that they won't get permission for revolt," Interior Ministry official Mahdi Alikhani was quoted by the official IRNA news agency as saying late Sunday.
Esmaeil Gerami Moghaddam, spokesman for Karroubi's National Confidence Party, countered on the party's website that under Iran's constitution there is no need for government permission to hold a peaceful rally.
Across central Tehran, riot police, many on motorbikes, fanned out to prevent any demonstration, witnesses said, speaking on condition of anonymity because of fears of reprisals from authorities.
The uprising in Egypt opened a rare chance for the political gambit by Iran's opposition.
Several opposition activists and aides to Mousavi and Karroubi have been arrested in recent days as part of government efforts to intimidate the opposition and undermine its resolve to hold a rally.
Ahmadinejad claimed the Egyptians who toppled President Hosni Mubarak took inspiration from Iran's 1979 Islamic Revolution, which brought down a Western-backed monarchy. Iran's opposition movement used the comments to push the government into a corner and request permission to march in support of Egypt's protesters.
Iranian officials quickly backpedaled and said no pro-Egypt rallies were allowed - bringing sharp criticism from the White House and others.
On Thursday, White House national security spokesman Tommy Vietor said: "For all of its empty talk about Egypt, the government of Iran should allow the Iranian people the same universal right to peacefully assemble and demonstrate in Tehran that the people are exercising in Cairo."
Karroubi and Mousavi have compared the unrest in Egypt and Tunisia with their own postelection protest movement. Mousavi said Iran's demonstrations were the starting point but that all the uprisings aimed at ending the "oppression of the rulers."
Turkish President Abdullah Gul, who is on a visit to Iran, urged governments in the Middle East to listen to the demands of their people.
"When leaders and heads of countries do not pay attention to the demands of their nations, the people themselves take action to achieve their demands," IRNA quoted Gul as saying Monday.
Hundreds of thousands of Iranians peacefully took to the streets in support of Mousavi after the June 2009 vote, claiming Ahmadinejad was re-elected through massive vote fraud.
A heavy government crackdown suppressed the protests. The opposition has not been able to hold a major protest since December 2009.