TEHRAN, Iran — Chanting a bitter new rallying cry, thousands of Iranians marched through Tehran Thursday in the latest protest over last month's disputed presidential election, but riot police fired tear gas and blocked them from reaching their intended goal of Tehran University.

"Mojtaba, we wish you dead, and never to become the leader," was the new cry in the streets, referring to the son of supreme leader Ayatollah Ali Khamenei. According to many analysts, Khamenei's son holds the real power in Iran and along with Ayatollah Mohammad Taqi Mesbah Yazdi was responsible for a virtual coup before the votes were counted to keep President Mahmoud Ahmadinejad in office.

Riot police blocked the main streets of Tehran and dispersed protesters with tear gas, pepper spray and metal clubs, and the Basij, the militia that's been at the forefront of the Iranian government's attempts to crush the opposition, threatened demonstrators and in some cases struck them. A McClatchy Newspapers special correspondent heard weapons fire and saw people being removed by ambulance but did not see anyone killed.

Witnesses reported more than 30 people were arrested in Ferdowski square, one of the main squares of central Tehran.

Videos reportedly taken on Thursday and appearing on anti-government Web sites showed thousands of protesters marching peacefully down a major thoroughfare and halting and splintering when police fired tear gas canisters into their ranks. The protesters were of all ages, and included women in chadors; many wore sunglasses to conceal their identity and handkerchiefs to cover their mouths.

The march was to commemorate student protests that occurred 10 years ago, which ended in a police raid of student dormitories in the University of Tehran. At the time it was the biggest anti-government demonstration since the 1979 Iranian revolution, and protests have been held on July 9 since then.

Thursday's was one of the smallest public protests since the disputed June 12 election in which opposition leader Mir Hossein Mousavi was supposedly defeated by Ahmadinejad, but the anger and determination of the participants in the face of an enormous crackdown showed that the authorities are unable to maintain control.

Thursday's protests took place despite direct threats by Morteza Tamaddon, the governor of Tehran, who threatened to "crush" the demonstrators.