The Iranian authorities have clamped down hard in anticipation of possible trouble on Wednesday, the anniversary of the raid on a student dormitory that sparked five days of street riots in Tehran and other cities four years ago.
Authorities are keen to avoid the violence that has marked previous anniversaries
Student organisations had planned to hold rallies to mark the anniversary and to protest against the arrest of many of their leaders in recent weeks. But no permits have been issued, and the Interior Ministry has circulated orders to local authorities to deal with any "illegal gatherings".
University campuses and dormitories have been cleared, with students being sent home early for the summer break and being told they could sit their year-end exams in September instead.
On Wednesday morning, the gates at Tehran University were locked, and only the gardeners were still on campus.
Student organisations had planned to hold a sit-in and hunger strike at the university mosque.
Dozens of student leaders have been detained recently on orders of the judiciary.
Many of them said they played no part in the 10 days of nocturnal street disturbances that broke out in mid-June, leading to an officially-admitted 4,000 arrests. Authorities say at least 2,000 people are still being held.
Student organisations had also been planning to hold a demonstration outside the Tehran headquarters of the United Nations.
Earlier, the biggest student group, the Unity Consolidation Office, had written a lengthy appeal to the UN Secretary-General saying it had despaired of the reformists and asking him to investigate "cases of human rights violations by the Iranian Government".
But the students agreed to call off all protests after an intervention by reformist members of the Iranian parliament, who told them their demands would stand a better chance of being met - and their leaders of being freed - in an atmosphere of calm.
Despite their compliance, three more student leaders were detained immediately after giving a news conference on Wednesday morning to explain why they had called off their visit to the UN headquarters.
Reza Ameri-Nassab, Arash Hashemi and Ali Moqtaderi were intercepted by plain-clothes gunmen as they left the building, and taken away with pistols at their heads. One of them is believed to have had his nose broken as he was being detained.
"If I am arrested today, I don't guarantee that I won't come out with confessions against myself after they've held me for a while, because of the pressures they put people under," Ameri-Nassab told journalists only minutes before he was seized.
The legality of such snatches, carried out on the orders of the Tehran public prosecutor Judge Saeed Mortazavi, has been challenged by student leaders and reformist officials and has become one of the main student grievances.
Student arrests have sparked demonstrations
The authorities have also taken steps to silence the radio and TV stations run from California by Iranian exiles bitterly hostile to the Islamic regime. Residents who defy the ban on satellite dishes and watch the broadcasts said they had been jammed for several days.
Several of the stations had openly incited Iranians to rise up against their rulers.
During the 10 days of disturbances in June, some people said they had attended demonstrations because they had heard about them from the stations.
Although neither the student organisations nor the reformist movement are backing streets protests, some ordinary people said they would turn out on Wednesday night to signal their defiance.
"Maryam", who supports Reza Pahlavi, son of the deposed Shah, said she was not deterred by the clubbing she received at the hands of riot police during the June demonstrations.
"I have lost my fear, and am more determined than ever to pursue this course until we achieve our goals, even if it costs me my life," she said.
But others who also took part in the demonstrations doubted that they would get anywhere.
"However hard people may try, nothing will come of it - apart from young people getting together and letting off steam," said one. "That's all it is. I don't think it will turn into anything serious."