In a protest against Iran's hard-line judiciary, hundreds of Iranian students today called for the release of political prisoners.

The political demonstration, Iran's largest in more than three years, coincided with mounting tension in this country of 65 million people as pro-reform President Mohammad Khatami seeks to break the stranglehold on power of conservative opponents at the heart of the political system.

Witnesses said that about 500 students made fires outside the gates of Tehran University and chanted: "Freedom of thought forever!" and "Our problem is the judiciary!"

Police blocked roads around the campus and fired at least one tear gas canister. But they made no move toward the students.

The demonstration came just days after a hard-line court sentenced reformist Tehran University academic Hashem Aghajari to death for blasphemy after he questioned the clergy's right to rule the Islamic Republic.

Elected in 1997 and reelected in 2001 in landslides, Khatami has found his efforts to promote democracy blocked by conservative rivals who control the judiciary, armed forces and broadcast media.

Khatami has introduced two bills in parliament aimed at limiting the power of the judiciary and curbing the veto power of the conservative Guardian Council over election candidates.

Aghajari, a 45-year-old history lecturer who lost a leg in the 1980-1988 Iran-Iraq war, angered the conservative clergy in a speech earlier this year in which he said Muslims were not "monkeys" to blindly follow the teachings of senior clerics.

His death sentence, issued after a closed trial without a jury, has been widely condemned both inside Iran and abroad.