Police officials declared that anyone who wishes to hold a protest, rally, or gathering must secure a permit, the police commissioner said.
Meanwhile, tens of thousands of President Ahmadinejad supports have reportedly been bused to Tehran in order to take part in pro-Ahmadinejad rallies. The signs carried by the protestors include "Death to America," "Death to the traitors," "Execute armed traitors," and various religious slogans.
Supports of defeated candidate, the reformist Mousavi, demonstrated nearby, holding their hands in the air quietly in silent protest. Observers expressed fears that the two rival camps may clash, but security forces were able to maintain order early on.
Limits on journalists
Earlier, Iranian authorities said they are restricting all journalists working for foreign media from firsthand reporting on the streets.
The rules cover all journalists, including Iranians working for foreign media. They block images and eyewitness descriptions of the protests and violence that has followed last week's disputed elections.
The order issued Tuesday limits journalists for foreign media to work only from their offices, conducting telephone interviews and monitoring official sources such as state television.
It comes as foreign reporters in Iran to cover the elections began leaving the country. Iranian officials say they will not extend their visas.
On the diplomatic front, Iran's Foreign Ministry summoned on Tuesday a senior Czech diplomat, representing the European Union, to protest against "interventionist and insulting" EU statements about Iran's election, the ISNA news agency said.
AP and Reuters contributed to the report