And the word still gets out, with amateur videos being posted on YouTube and shown to the world. BBC Persian reported receiving videos from viewers at the rate of five a minute Tuesday.
Both supporters and opponents of Ahmadinejad held separate rallies Tuesday in Tehran to either celebrate, or condemn, last week's contested elections.
Mousavi supporters gathered illegally to protest the election results. After initially encouraging his supporters to attend, Mousavi warned them away, fearing violence. Police said protestors would pay a heavy price.
"Our officers will crush any unrest," said Esmaeil Ahmadi Moqaddam, the national chief of police.
Demonstrators defied the threats. Some eyewitnesses reported crowds even bigger than Monday's massive demonstration, which drew hundreds of thousands.
"The protestors came to claim their rights," said one Tehran resident. "It's the government that should be held responsible."
Speaking on Iranian television, a member of the Guardian Council -- Iran's most powerful clerics -- offered a partial recount. But opposition leaders are demanding an entirely new election.
"I do not think the Guardian Council will have the courage to stand against the people," said Ali Akbar Mohtashamipou, a Mousavi representative. Iranian state TV announced Tuesday that Iran's supreme leader, Ayatollah ali Khamenei, met with envoys of four opposition candidates and called for unity.
Amateur video reportedly showed a long column of anti-government protesters walking, apparently peacefully along a wide street on Tehran's north side, not far from where the pro-government rally was being held.
In Washington, President Obama said Tuesday the Iranian government's decision to allow a recount of some of the votes in last week's election shows that Khamenei understands that the Iranian people have "deep concerns" about the election, and its bloody aftermath.
But Obama, speaking after a meeting with South Korea's president at the White House, continued to tone down his criticism of the government, saying it would be "not productive ... to be seen as meddling."
Officials prepared to recount ballots, but only from contested precincts, after a ruling by Iran's Guardian Council, controlled by Khamenei.
Ahmadinejad was declared the winner by "a large margin" in last Friday's election.
After Monday's protest, Iranian state radio said seven people were killed in clashes when "thugs attacked a military outpost" after a mass rally.
But ABC News witnessed the protest and it was very peaceful.
Unlike previous protests dominated by young people, Monday's protest mixed young and old, students and professionals.
A male protestor told us, "It's very clear, clear as daylight, you see the crowd. The government has really changed the results."
A female protestor chimed in, saying, "We're here for our revolution." Like many here, she expressed the hope that the demos could bring about a change in the government.
Mousavi supporters flooded through downtown Tehran, numbering hundreds of thousands, making this possibly the largest demonstration here since the 1979 Islamic revolution.
All was peaceful until early in the evening pro-government paramilitary fired into the crowd.
The shots came from the roof, an eyewitness told ABC News over the phone, hitting a car with protestors riding on top. One man was hit and flung from the car.