TEHRAN, Iran (CNN)  -- Iran's supreme leader is warning the thousands of people who have been protesting last week's presidential vote to maintain self-restraint or face a stiff reaction from authorities.





Ayatollah Ali Khamenei speaks to a crowd in Tehran during Friday prayers.





Members of the opposition -- who have staged noisy demonstrations for the last six days to protest what they believe was a rigged election -- are weighing their options after Supreme Leader Ayatollah Ali Khamenei drew a line in the sand during his all-important sermon during Friday prayers.





The supreme leader declared last week's presidential election a "definitive victory" for President Mahmoud Ahmadinejad and sloughed off charges of vote tampering.





"Any extremist move will fan up another extremist move," said Khamenei, who criticized the street protests and said those who caused violence during demonstrations would be held accountable.





"If the political elite want to ignore law and break the law and take wrong measures which are harmful willy nilly, they will be held accountable for all the violence and blood and rioting."





Khamenei called on those who don't believe the results to use proper legal avenues, such as requesting a recount they could observe.  Watch Khamenei deny allegations of vote-rigging »





He did not, however, issue a call for a new vote -- a move that opposition leaders such as Mir Hossein Moussavi have been demanding.





Instead, he passionately defended the election as he addressed a crowd at Tehran University.





The election is expected to be a topic of conversation on Saturday before the Guardian Council, which supervises the country's elections. A council official said the body has invited three candidates -- Moussavi, Mehdi Barrubi, and Mohsen Rezaie -- to its meeting to discuss any issues they see fit, according to the Islamic Republic News Agency.  Watch Khamenei defend the outcome of the election »





More protest rallies are planned for Saturday -- one sponsored by supporters of opposition candidates Moussavi and Karrubi and another by supporters of former President Mohammed Khatami. While both camps said they had no plans to cancel the marches, the Interior Ministry told FARS news agency there were no permits issued for either event.





Analysts and observers are now debating what will happen next as more developments emerged on Friday.





"We do not yet know whether Ahmadinejad will stay, whether Mousavi will somehow be given a second chance, and if the ongoing political struggle will affect the security of the Supreme Leader," Anthony H. Cordesman of the Center for Strategic & International Studies wrote in a paper published Friday after the speech.  Watch CNN's Christiane Amanpour describe what she saw while reporting on Iran election »





He said that it's clear Khamenei is backing Ahmadinejad and any review of the election will be under those loyal to the supreme leader. But at the same time, Khamenei "cannot put this genie back in the bottle."





"Whatever happens, if Ahmadinejad stays without a truly legitimate election, the result will fester, not go away. Every embarrassing new piece of excessive rhetoric, every new threat to Iran's neighbors, every new problem in the economy, and every new act of social repression will be a reminder of the fact that Iran's leadership has questionable legitimacy at best," Cordesman wrote.





Human rights monitor Amnesty International issued a statement on Friday saying Khamenei's sermon "indicates the authorities' readiness to launch violent crackdowns if people continue to protest which may cause a widespread loss of life."





"We are extremely disturbed at statements made by Ayatollah Khamenei which seem to give the green light to security forces to violently handle protesters exercising their right to demonstrate and express their views," said Hassiba Hadj Sahraoui, Amnesty's deputy director of the Middle East and North Africa program.





"If large numbers of people take to the street in protests in the next couple of days, we fear that they will face arbitrary arrest and excessive use of force, as has happened in recent days."





The group said Khamenei should have warned security to act with restraint.





"For a head of state to put the onus of security on peaceful demonstrators
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"Any extremist move will fan up another extremist move," have been protesting
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