A demonstration began at 12.30 by several hundred students with hundreds more pouring into the crowd.
Power lines are cut in local internet cafes in what appears to be a government-orchestrated action to prevent news of the protests from spreading. Most payphones in the area are also out of action.
Apart from the large uniformed-police presence, there are many plainclothes agents at the site of the university and in internet cafes.
The situation is reported to be tense and there is a possibility that clashes could erupt between chanting students and agents of the State Security Forces.
Late Tuesday, students from the University of Tehrans Engineering, Literature and Human Studies, Medical, Dentistry, and Chemistry Faculties issued a joint statement accusing the authorities of deliberately shutting down schools and universities in Tehran to prevent large-scale student protests on Students Day under the pretext of poor air quality.
Irans Majlis (Parliament) Speaker Gholam-Hossein Haddad-Adel gave a stark warning to students not to rise against the state. Student action against the regime is a ploy by the enemy, he said, adding, Students must never loose sight of the reality that they are the target of our enemies who have thousands of plots and ploys to use universities against the Islamic Republic.
Student protests have been on the rise in Iran in recent weeks in the run-up to the anniversary of the bloody suppression of a rally outside Tehran University in 1953.
On December 7, 1953, three students were shot dead by policemen during a rally against the Shahs dictatorship. The day has been named Students Day and commemorated on campuses across Iran every year.
