By Kay Biouki in Teheran and Gethin Chamberlain
Ebrahim Lotf-Allahi, a fourth year law student, was buried before his family could see his body.
They later discovered that the grave had been filled with cement, apparently to prevent his body being exhumed for medical examination.
Student leaders say 150 students have been arrested so far this year and 60 remain in prison.
Iranian authorities claim that Mr Lotf-Allahi committed suicide after he was arrested in the city of Sanandaj, but his is the second suspicious death in custody in the city in just over a month.
In December a young woman doctor, Zahra Bani Yaghoub, died after she was arrested for walking in a park with a man to whom she was not related.
Her family say that bruises on her body suggested she had been beaten while in custody.
Sources in Sanandaj said Mr Lotf-Allahi was picked up as he left his universitys examination hall and that when his family went to arrange for him to be released from custody, they were told that he has committed suicide.
His death has angered student activists, who believe it is part of a campaign of harassment aimed at supressing dissent before the March elections.
They say students in the Kurdish part of the country, which includes Sanandaj, have borne the brunt of the crackdown.
Ali Nikoo-Nesbati, a student who was released from custody last month after 35 days in solitary confinement, said Iranian officials had targeted minorities, including the Kurdish population, who were trying to stand up for their rights.
“Surely in this case human rights have not been practised?” he said. “When you are in custody your life must be secured by the government, and no-one accepts that Lotf-Allahi committed suicide.”
He said students only wanted to be treated humanely.
“They only want their basic needs. They are not criminals, but instead of solving their problems the government puts them in jail and confronts them in ways that are hard to explain,” he said. “We will resist and we will not pull back – if we pull back now we lose everything.”
Opponents of the Iranian regime have complained that they have been the victims of a crackdown by hardliners in the run up to the elections.
Last week it emerged that about 2,000 of the 2,500 reformist candidates planning to stand had been barred from participating.
The National Trust Party, headed by Ayatollah Karoubi, a presidential candidate at the last elections, had 230 out of its 300 applications rejected while Saeed Shariati, spokesman for the the Islamic Participation Front, said the vast majority of its candidates had been disqualified.
“The governing body disqualified 85 per cent of our candidates for unbelievable reasons,” he said.
