Numbers were hard to assess, given government threats against journalists who tried to cover the protests. Aliakbar Mousavi Khoeini, a former member of Parliament now living in exile in the United States, said that 20,000 to 30,000 people had taken part across the country.

Ayatollah Khamenei and the Iranian establishment have tried to depict the Arab movements as a long-awaited echo of the 1979 Islamic Revolution, though Islamist parties had a low profile in both the Egyptian and Tunisian uprisings. The Iranian opposition has painted the Arab protests as an echo of its own anti-government movement in 2009, when citizens demanded basic rights like freedom of assembly and freedom of speech after the disputed re-election of President Mahmoud Ahmadinejad.

Mehdi Karroubi, an opposition leader, said in an interview last week that the opposition had decided to organize a day of demonstrations to underscore the double standard of the government in lauding protesters in Arab countries while suppressing those at home. Mr. Karroubi has been put under house arrest, with outside communication links severed, opposition reports said, as has Mir Hussein Moussavi, the other main opposition leader.

The Fars news agency, a semiofficial service linked to the Islamic Revolutionary Guards Corps, indirectly confirmed the protests by saying an unspecified number of demonstrators had been arrested. It called participants “hypocrites, monarchists, ruffians and seditionists” and ridiculed them for not chanting slogans about Egypt, the nominal reason for the protests.

The authorities’ tactics on Monday indicated that they were resolved to stifle unrest — starting with the refusal to issue a permit for a nationwide demonstration. Reports that did emerge suggested that security forces had tried to prevent people from gathering by blocking the access routes to main squares in major cities and closing train stations in Tehran.

The crackdown came as the protests flared in Yemen and Bahrain. While those outbreaks were reported in some official Iranian state news media, which had also covered the 18-day Egyptian uprising selectively, there was no immediate mention of the clashes in Tehran and elsewhere on such state broadcasters as the English-language Press TV in Tehran.

Iran’s Islamic government gradually stamped out the 2009 protests through the shooting of demonstrators, mass trials, torture, lengthy jail sentences and even executions of those taking part.