"According to the local justice and intelligence reports he had hanged himself in his cell. The definitive reason of his death is being examined," judiciary spokesman Ali Reza Jamshidi said.

The family of Ebrahim Lotfolahi, who was a fourth-year law student, have cast doubt on his alleged suicide, demanding an exhumation and probe, their lawyer Saleh Nikbakht said.

"An exhumation will be carried out if the judge thinks it is needed," Jamshidi said of the student who died on January 15 after nine days in the jail of Kordestan province.

A prominent human rights group headed by Nobel laureate Shirin Ebadi have also called for an investigation, citing his "hasty burial by officials and preventing the family and their trusted doctor from examining the body."

Jamishidi said that Iran currently held 19 students in jail, but that eight would be released soon.

"Out of 19 jailed students preliminary investigations have been completed for eight and they will be released within the next days on bail," he said, adding that a group of 11 students had also been recently released.

Iranian authorities have arrested dozens of students in the past months at demonstrations staged in main universities where students called for the release of jailed colleagues and criticised President Mahmoud Ahmadinejad.

The controversial detention since May of three students from Tehran's Amir Kabir University has become a major issue for protesters.

Ahmad Ghassaban, Ehsan Mansouri, Majid Tavakoli remain in jail despite posting bail and being acquitted of serious charges including insulting Islam, their lawyer Mohammad Ali Dadkhah said.

Ahmadinejad was famously heckled in 2006 during a speech to students at Amir Kabir, one of Iran's most prestigious institutions which has long been a hotbed of political activism.