CAIRO — Tehran's police chief said Friday that few arrests were made in opposition protests that erupted a day earlier in the Iranian capital in an opposition attempt to revive street demonstrations over the country's disputed election.

The lack of an overwhelming crackdown — despite authorities' vows to "smash" anyone who joined the marches — could suggest the country's leadership is hoping Thursday's protests would be a one-time event and will subsequently weaken.

Several thousands demonstrators marched down Tehran's main avenues in Thursday's protests, chanting "down with the dictator" and slogans in support of Mir Hossein Mousavi, the pro-reform candidate who contends he was defrauded of victory in June 12 presidential elections.

In some locations around the city, police clashed with protesters, charging at them and beating them with batons or firing tear gas, sending young men and women running through choking clouds. But the clampdown was not total, and in some locations, security forces were in heavy numbers but allowed protesters to demonstrate.

The protests, which organizers had planned for one day only, died down by Thursday night, and on Friday there were no demonstrations.

"The number of those arrested was very few, and there was no widespread campaign of arrests," Tehran police chief Azizullah Rajabzadeh told the semi-official Mehr news agency. He said those detained were involved in "instigating the damaging of public property and chanting."

Rajabzadeh did not give an exact number of arrests.

Pro-reform Web sites reported that members of the Basij, a paramilitary militia that has been involved in putting down protests, stormed into a dormitory of Amirkabir University Thursday night and attacked students. The university is a prominent center for pro-reform student activists.

In the attack, which took place as the day's street protests were winding down, plainclothes Basijis broke into the dormitory, beat students and set off tear gas, according to reports on several Web sites citing university students. They said a number of students remained unaccounted for after the assault. Officials could not be reached Friday to comment on the reports.

Thursday's marches were the first in nearly two weeks, and were an attempt to revive protests after a heavy security crackdown crushed the massive rallies that erupted over the elections. In those rallies, hundreds of thousands took to the streets, rejecting official results that showed a landslide victory for incumbent hard-liner Mahmoud Ahmadinejad.

Supreme leader Ayatollah Ali Khamenei, who holds ultimate say in the country, eventually declared the vote valid. But Mousavi has said he will persist in his campaign against a government he says has no legitimacy.