Crowds of pro-regime backers were expected on Tehran streets after Friday prayers to condemn the "treacherous" opposition chiefs who officials say have rebelled against Iran's Islamic establishment.
Worshippers were expected to stream out of Tehran University after the weekly prayers and join other regime-backers in denouncing opposition leaders Mir Hossein Mousavi and Mehdi Karroubi, former pillars of the Islamic regime.
Those joining the rally will "scream out their hatred, wrath and disgust against the savage crimes and evil movement of sedition leaders, their Monafeghin (hypocrites) and monarchist allies," said the Islamic Propagation Coordination Council, the body organising Friday's marches.
The Tehran Friday Prayer Committee said the rally "will condemn the treacherous and disgraceful actions of opposition heads and their agents," the state television website reported.
The latest outburst against the two leaders and their supporters erupted after they held an anti-government protest on Monday under the pretext of showing solidarity to Arab uprisings.
The Monday rally, banned by authorities, turned into deadly clashes between protesters and riot police in which two people were killed and several wounded, including nine members of security forces, reports said.
The protests were the first after the one held on February 11 last year on the day Iran was marking its 31st anniversary of the Islamic revolution.
That demonstration too like several other earlier ones was crushed by security forces and militiamen.
Mousavi and Karroubi are under de facto house arrest but have regularly issued messages to their supporters through their websites which has fuelled the anti-government demonstrations.
The latest protest has infuriated regime backers, top officials and lawmakers who even demand execution of Mousavi and Karroubi.
"The treason committed by the movement of sedition leaders is not hidden from anyone," Iran's chief of judiciary Ayatollah Sadeq Larijani was quoted as saying by state news agency IRNA Thursday.
"This group which has rebelled against the religious government should know that while maintaining Islamic compassion we will not tolerate the establishment being compromised."
Larijani said steps were being taken by the judiciary against the two and that the authorities were targeting their communication networks.
"They (the people) should be certain that we will block the mechanism through which the sedition leaders issue their statements," he said.
But defiant supporters of Mousavi and Karroubi have called for new nation-wide rallies Sunday to mourn the deaths of the two slain in Monday's protests by mobilising supporters through the Internet.
The Sunday rallies are also intended to show "decisive support" to Mousavi and Karroubi for "continuing on the difficult path of freedom and human dignity," the Council for
Coordination of the Green Movement Hope said in a statement on Kaleme.com and Sahamnews.org, websites of Mousavi and Karroubi.
Referring to the two victims of Monday's protests, it said the rallies will "also show solidarity with our Kurdish countrymen in honouring the blood of these two dear Sunni and Shia Iranians which was spilled while fighting religious tyranny."
The simmering tension between pro-regime and anti-regime forces is reminiscent of the unrest which followed the June 2009 presidential election which saw hardliner Mahmoud Ahmadinejad return to power.
Dozens of people were killed, scores wounded and thousands arrested when authorities cracked down on anti-Ahmadinejad protesters in 2009, leading them to adopt, until Monday, a much lower profile.
Mousavi and Karroubi, who lost to him in the poll, maintain that Ahmadinejad was fraudulently re-elected and since then have opposed his presidency.
On Wednesday, Karroubi and Mousavi issued Internet statements in which the former said he was "ready to pay any price", while Mousavi stated that Monday's protests were a "glorious achievement."