Supporters of Iran opposition leader Mir Hossein Mousavi are protesting in the capital Tehran for the fourth straight day over the disputed presidential election.
Mr Mousavi called his followers back onto the streets of Tehran for another mass rally over the disputed presidential election and urged them to wear black to mourn those killed in clashes.
The call for opponents of President Mahmoud Ahmadinejad to rally again was in open defiance of the country's supreme leader, who has urged the nation to unite behind the Islamic state.
It came a day after tens of thousands marched silently down a main street of the capital, brandishing posters of Mr Mousavi and waving V-for-victory signs, amateur video showed. Some covered their mouths with masks.
International news organisations have been banned from covering the protests over last Friday's election, which the government declared hard-line President Mahmoud Ahmadinejad won by a landslide.
Mr Mousavi and his supporters claim Friday's election was rigged and he was the true winner.
On Monday, hundreds of thousands turned out in a huge procession that recalled the scale of protests during the 1979 Islamic Revolution. Seven demonstrators were shot and killed that day by pro-regime militia in the first confirmed deaths during the unrest.
The protest would be the fourth straight day of major marches in the capital - rallies that recalled the unrest three decades ago that brought down Western-backed Shah Mohammad Reza Pahlavi and propelled the Islamic clergy to power.
The street protests have presented one of the gravest threats to Iran's complex blend of democracy and religious authority since the system emerged out of the Islamic revolution.
But the chances of bringing down the Islamic system appear remote. The ruling clerics still command deep public support and are defended by Iran's most powerful military force - the Revolutionary Guard - as well as a vast network of militias.