Tamaddon was quoted by Irna, the official news agency, as saying that the government is responsible for the security of the population and of society, and that it had not issued a permit for the demonstration. "If some people want to act under the influence of anti-revolution TV channels, they will be crushed under the steps of our vigilant people," he said.

Mousavi apparently didn't participate in Thursday's demonstration, and an aide said his followers are "worried about his life."

However, Mohsen Makhmalbaf, Mousavi's campaign manager in the June polls, said the latest protest, which linked the student-led movement of 1999 with the "green movement" that sprang up on the eve of the presidential elections, will continue regardless of what happens to Mousavi.

"Every Iranian is a campaign headquarters himself. Every Iranian has to be both a follower and a commander for this movement," said Makhmalbaf, who spoke to reporters by phone from France. "We are prepared in the case that the government imprisons Mousavi, we will not consider this movement finished. This movement will go on."

He said Mousavi was "one ring in this chain. In the event that we lose him as a leader, this chain will not be lost."

Editor's note: McClatchy Newspapers is not identifying its correspondent in Tehran due to security considerations.