"There are hundreds of riot police, (they are) everywhere around Tehran University and nearby streets," said the witness, who asked not to be named.
Iran commemorates on Monday the killing of three students in 1953 under the former Shah. The opposition is expected to use the state-organised rallies in the country to revive protests against June's disputed presidential election. Iran on Saturday banned foreign media from reporting on the Student Day rally.
Police and elite Revolutionary Guards have warned that any "illegal" rally will be fiercely confronted.
