A protester was killed during intense clashes between pro-democracy supporters and security forces in central Tehran yesterday, opposition reports said.
Some unconfirmed accounts said three were killed. Officials insisted there were no deaths.
Yesterday's protests were called to commemorate the deaths of two opposition supporters killed in clashes last Monday when tens of thousands of pro-democracy demonstrators, galvanised by the uprisings in Egypt and Tunisia, rallied on the streets for the first time in a year.
Even more protesters were said to have turned out yesterday, mobilised by young opposition supporters via Facebook.
Forewarned, security also mustered a far greater show of strength. They used live ammunition in a Tehran square, an Iranian human-rights group and independent witnesses said.
As night fell and rain washed away clouds of tear gas, the opposition crowds swelled. They chanted "Allahu Akbar" (God is Greatest) and slogans calling for the overthrow of the "dictator", referring to Iran's supreme leader, Ayatollah Ali Khamenei. There was a surge outside the heavily defended headquarters of the state broadcaster, which has vilified opposition leaders as "seditionists" allied to the United States, Britain and Israel.
Some official media claimed there was "calm" in the Iranian capital and maintained the roads were clogged because people were out shopping in preparation for the Iranian New Year.
Iran's state-run news agency, however, indirectly acknowledged there was unrest by reporting that the daughter of Iran's former president, Akbar Hashemi Rafsanjani, was arrested for taking part in a banned opposition rally.
"Faezeh Hashemi Rafsanjani was identified and arrested by security forces in Tehran while … making blunt statements and chanting provocative slogans," Irna said. She was later released, official media said.
Her father, a two-time president and cleric, was a founder of the Islamic republic and one of Iran's wiliest politicians who still holds highly influential posts. He is a bitter opponent of the president, Mahmoud Ahmadinejad.
There were credible reports of unrest in other major cities, including Mashad, Isfahan, Tabriz and Rasht.
But the size of protests and the extent of casualties were impossible to ascertain immediately because foreign media were banned from covering opposition gatherings.
The opposition, growing in inventiveness, flooded busy highways with cars to prevent security men on motorcycles from rushing to scenes of unrest.
In turn, the authorities disconnected cell phone lines in central Tehran curbed internet speed in an attempt both to prevent bad news getting out and disrupt communication between demonstrators.
The protests were also a show of support for the Green movement's two main leaders, Mir Hossein Mousavi and Mehdi Karrubi.
The two men, who both challenged Mr Ahmadinejad in the controversial election of June 2009, are under unofficial house arrest. Hardliners have called for them to be tried and executed.
Both men, once pillars of the Islamic republic, have so far acted as leaders of the opposition, committed to reforming the system, not overthrowing it. But as the chants against Ayatollah Khamenei indicate, many of their increasingly radicalised young followers believe the system is beyond reform.
"Most of the protesters seem to want a secular state and I think Mr Mousavi and Mr Karrubi will tacitly back them in this," said an analyst in Tehran, who declined to be named. "It is now the people who are leading the leaders, not the other way around."
