The Facebook page of Iran's top opposition presidential candidate quoted him Saturday as saying he is preparing to die and urging his followers to go on strike if authorities arrest him.
Mir Hossein Moussavi, who has led a protest against the government over last week's election, said he is preparing himself for "martyrdom" and is quoted as telling supporters to "protest" and "not go to work."
The authenticity of the message could not immediately be established.
Security police made "a very large show of force" in midtown and southeastern Tehran, using tear gas and clubs to beat back protesters as clashes erupted during the unrest.
This comes as demonstrators emerged on city streets to protest last week's elections in defiance of supreme leader Ayatollah Ali Khamenei's Friday pronouncement that protests must end.
Police fired guns in the air, and Iran's Press TV also reported the use of water cannons to disperse protesters. Uniformed and plainclothes police were deployed around Revolution Square, the site of a major planned demonstration, and traffic was being turned away on a major thoroughfare leading to the square, a witness said.
The forces confronted demonstrators who tried to avoid the thoroughfare and take side streets toward the square. Clashes erupted as forces used clubs to beat back protesters. Cell phone service was brought down after 5:30 p.m. in the area, witnesses said. Police told protesters they had no permit to protest.
Police also said Saturday that 400 security forces had been injured during the week's heavy demonstrations, and that public property had been damaged, Press TV reported.
Three camouflaged men with shields were seen pushing a man in the opposite direction. The number of people on the streets and the traffic appears less than normal, but daily life is going on.
A few thousand people who attempted to enter the site of a major planned demonstration in Tehran were blocked by heavily armed police, a witness said.
Another witness said he was walking through a central square when he saw about 200 men with the Basiji militia, a security force that takes orders from the Iranian government. With some wearing government-issued helmets and shields, their presence was a hint of an ominous security presence.
Elsewhere, another witness said hundreds of protesters were walking a mile from Revolution Square when some militia men dropped two tear gas canisters among the crowd to apparently dissuade them from gathering.