Rallies started Friday throughout Iran to mark the 32nd anniversary of the 1979 Islamic Revolution.
Millions of people were expected to attend the state-organized demonstrations, according to state television.
President Mahmoud Ahmadinejad was expected to make a speech at Azadi (Freedom) Square in western Tehran.
The rallies this year were also supposed to be an act of solidarity with the people of Egypt and their protests against President Hosny Mubarak's government.
Iran's opposition also wanted to use the protests in Cairo to hold its own demonstration Monday in solidarity with the Egyptian people.
The government and judiciary rejected the plan, saying the opposition could voice their solidarity in the anniversary demonstrations.
Observers said they believe the opposition expected the rejection but its main aim behind the rally plan was to show that although Iran supports the Egyptian protesters, the establishment would not grant its own people the right to protest, ISNA reported.
The government cracked down on mass opposition rallies after the 2009 presidential election, in which Ahmadinejad was re-elected amid widespread accusations of election fraud.
On the eve of the anniversary rallies, the government arrested several dissidents, including the former social welfare minister of reformist president Mohammad Khatami, opposition websites sahamnews reported.
The websites also said one of the main opposition figures, Mehdi Karroubi, was under house arrest, reportedly to prevent him from organizing any protests on the anniversary.
None of the reports by the opposition websites were confirmed by officials.
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