Iranian police have dispersed hundreds of protesters who staged a march to commemorate the anniversary of student unrest in 1999, witnesses have said.
Police fired tear gas on Thursday to scatter demonstrators who defied government warnings and moved towards Tehran University, the centre of the unrest 10 years ago.
Police in riot gear were out in force due to earlier street protests that had been held against last month's presidential election.
One student, who was at the protest but wanted to remain unnamed, told Al Jazeera: "They were starting to have a very calm demonstration, but the police started hitting the people, arresting the people.
"They didn't let anybody to go near the Revolution Square the main point of the student demonstration.
"Also the people riding their cars - you can hear them using the sound to protect the people who march in the street. If the police see any cars making the sound, they get the ID and didn't let them to go anywhere."
The Iranian authorities had said that any commemoration of the 1999 incident, in which at least one student was killed and dozens wounded when vigilantes stormed a university dormitory, would be dealt with forcefully.
The warning was issued after the G8 leaders expressed "serious concern" over the last month's post-election unrest which left at least 20 people dead.
Groups of students have held small commemorative gatherings in previous years, but Morteza Tamadon, the governor of Tehran, issued a blunt warning for this year's anniversary.
"If some people make moves that are contrary to security initiatives under the influence of anti-revolutionary networks, they will be trampled under the feet of our alert people," he told the official IRNA news agency.
Witnesses said leaflets had been handed out in several Tehran squares urging people to join Thursday's gathering.
The Iranian authorities have banned all gatherings amid a crackdown on protesters, reformists, journalists and political activists who have opposed the re-election of Mahmoud Ahmadinejad.