Around 1,000 pro-reform Iranians gathered in a central Tehran square on Monday as a senior Iranian politician said the ground was ready to legally pursue the moderate defeated presidential candidate Mir Hossein Mousavi for the illegal protests.
"Mousavi's calling for illegal protests and issuing provocative statements have been a source of recent unrests in Iran ... Such criminal acts should be confronted firmly," said Ali Shahrokhi, head of parliament's judiciary committee, semi-official Fars news agency reported.
"The ground is paved to legally chase Mousavi," he said shortly after the elite Revolutionary Guards warned they would crack down on any election-related unrest.
Witnesses said protesters were gathering late in the afternoon and riot police were trying to disperse them.
Mousavi had urged supporters Monday to stage more protests over the re-election of hard-line President Mahmoud Ahmadinejad.
Mousavi made a veiled appeal to the security forces to show restraint in handling demonstrations -- a move likely to be viewed with deep suspicion by a conservative leadership that has vowed to use force wherever necessary to quell opposition.
State radio said on Monday that the capital had been calm overnight for the first time since the June 12 election.
Mousavi, 67, reiterated his demand for a new election, and told his supporters on Sunday: "The revolution is your legacy. To protest against lies and fraud is your right. Be hopeful that you will get your right and do not allow others who want to provoke your anger... to prevail."
"In your protests, continue to show restraint. I am expecting armed forces to avoid irreversible damage," he said.
The revolution is your legacy. To protest against lies and fraud is your right. Be hopeful that you will get your right and do not allow others who want to provoke your anger... to prevail
Iranian state radio said at least 457 people were arrested in the violent clashes in Tehran on Saturday that killed between 10 and 13 people wounded 100.
State television said a daughter of former president Hashemi Rafsanjani, a rival of Ahmadinejad, had been released after being detained together with four other relatives during the Saturday rally in Tehran.
The authorities have branded the protesters as "terrorists" and rioters. Tehran's police commander Azizullah Rajabzadeh said police would "confront all gatherings and unrest with all its strength," the official IRNA news agency reported.
Gunfire and chanting
In pro-Mousavi districts of northern Tehran, supporters took to the rooftops after dusk Sunday to chant their defiance, witnesses said, an echo of tactics used in the 1979 revolution.
There were no immediate reports of casualties and the shooting appeared an attempt to break up unsanctioned protests.
Government restrictions prevent correspondents working for foreign media from attending protests to report. Iran closed Al Arabiya's Tehran bureau and ordered BBC correspondent, Jon Leyne, out of the country.
Analysis shows "irregularities"
Independent British think tank Chatham House said the election results show "irregularities" in the turnout and "highly implausible" swings to President Mahmoud Ahmadinejad, according to an analysis published on Sunday.
It said that in a third of all provinces, official results would have required Ahmadinejad to take all former conservative, centrist and all new voters, and up to 44 percent of reformist voters, "despite a decade of conflict between these two groups."
There would have to have been a radical shift in rural voting patterns and a "highly unlikely" change in heart among former reformist voters for Ahmadinejad to win as he did, the study concluded.
The authorities reject charges of election fraud. But the highest legislative body has said it is ready to recount a random 10 percent of votes cast.
Air force exercises
Meanwhile Iran began three days of airforce exercises in the Gulf and the Sea of Oman that were planned last month to raise operational and support capability, Iranian media said.
State broadcaster IRIB's website said the exercises were also aimed at raising the force's ability to use intelligence aircraft "to send signals and analyse threats" but did not mention Iran's disputed presidential election in its report.
Iran often holds war games or tests weapons to show its determination to counter any attack by the United States or Israel on sites where they believe nuclear weapons are made.