Hundreds of Iranians on Thursday afternoon gathered near Tehran University where security forces and anti-riot police maintained a strong presence. The renewed demonstrations were called to mark the 10th anniversary of the 1999 student protests in the country.
According to Press TV, Iranian security forces fired rounds of tear gas to break up the protesters.
Tehran police had earlier warned people against participating in any rallies in the city, adding no permit had been issued for any such demonstrations.
Small crowds of protesters also gathered in other sites in the Iranian capital.