Students across Iran are planning to lead a huge day of protest this week against President Mahmoud Ahmadinejad's regime, in a defiant commemoration of the 30th anniversary of the US embassy takeover by radical students in Tehran.

Thousands of green flyers and posters, drawn by anonymous artists, are circulating on the internet, inviting ordinary Iranians to join the student protests, planned for Wednesday.

Organisers have condemned the repressive measures taken by Ahmadinejad's government since the disputed election results of the summer, which gave the Iranian president a second term and led to unprecedented demonstrations on the streets of Tehran and elsewhere. Opposition leader Mir Hossein Mousavi appeared to back the protests yesterday, posting a statement on a reformist website. Mousavi said he would press ahead with his efforts for political change.

Referring to the Iranian date of the seizing of the US embassy in 1979, Mousavi said: "The 13th of Aban is a... rendezvous so we would remember anew that among us it is the people who are the leaders."

Iran's police chief, Ismail Ahmadi-Moghadam, has warned demonstrators to stay off the streets, but activists predict one of the biggest days of protest since the height of the green marches.

A student of civil engineering at Amir Kabir University in Tehran, who wished to remain anonymous, said: "The officials are very afraid of the student movement, that's why they are preparing to crack down on 4 November. The protests in Iran have not cooled off, they're just beginning."

Iran's students were on vacation during the failed "Green Revolution" of June, when hundreds of thousands of protesters attempted to overturn the official election result, which gave Ahmadinejad a crushing victory over Mousavi.

But in recent months, despite the high-profile presence on campuses of security police, universities have become centres of underground protest and organisation. Dissent has also been expressed in schools. One teacher in a Tehran school told the Observer that such gestures of rebellion were widespread.

"It is amazing," he said, asking not to be named. "In the school where I'm teaching, students show their opposition in any way that they can find, whether it's by wearing a green wristband, green shirt, doing homework in green pen or writing slogans in toilets, on their desk or on the blackboard."

In an interview published on the Amir Kabir University student news website, Morteza Simiari, a leader of Iran's Student Organisation, Tahkim Vahdat, said: "The students who are protesting in universities today are the people who were out there in the streets in June and July and were mistreated. Universities are part of society and what is happening now shows that people do not believe the results in the election."

Authorities have closed 235 schools in Kashan, in the province of Isfahan, until Saturday, ostensibly as the result of a swine flu scare, although no cases of the virus have been reported.

Since the beginning of the academic year in Iran, students in Tehran, Isfahan, Shiraz, Karaj, Qazvin and other provincial cities have all held protests against the election results. Hundreds of students have as a result been summoned before disciplinary boards, some have been imprisoned and at least 20 expelled.

Government officials visiting universities have received stormy receptions. On 4 October, Mohammad Javad Larijani, a close ally of Ahmadinejad, visited Sharif University, where he was confronted by students shouting "Death to the dictator" and chanting in favour of Mousavi.

In Tehran, the private Azad University has been a hotbed of unrest, according to students. "Azad university protests were huge, so they [the authorities] used tear gas and wielded batons to calm down the situation," said one of the Azad protesters. "They bussed in militia from other universities. Recently 14 of us have been banned from class."