Police in Iran have dispersed hundreds of demonstrators who defied government warnings that any fresh attempt at protests would be "smashed".
Tear gas was used. The marchers were heading towards Tehran University to commemorate the 10th anniversary of student unrest in 1999 against the Basij militia.
Small student-led groups have commemorated the event every year since then.
The BBC reports a number of smaller demonstrations also took place in provincial cities.
All gatherings have been banned in a crackdown on mass protests that erupted after a disputed presidential election on 12 June.
Incumbent Mahmoud Ahmadinejad was declared the winner with 63% of the vote.
There has been no major protest for nearly two weeks and Tehran Governor Morteza Tamaddon warned earlier no more would be tolerated.
Meanwhile, another member of a group headed by the Nobel Peace Prize winner Shirin Ebadi has been arrested.