Iran's powerful Revolutionary Guard said yesterday that opposition leader Mirhossein Mousavi, a defeated presidential candidate and former president, should be tried for inciting unrest after the disputed presidential poll.

The June 12 election plunged Iran into its biggest internal crisis since the 1979 Islamic revolution, exposed deepening divisions in its ruling elite and set off a wave of protests that left 26 people dead.

Protests gripped Tehran and other cities after the vote, which moderates say was rigged to secure the re-election of President Mahmoud Ahmadinejad. State media say at least 26 people were killed and hundreds arrested in post-election violence.

In an attempt to uproot the opposition and end street protests, Iran began two mass trials of moderates, including several prominent figures charged with offences that included acting against national security by fomenting voter unrest.

Meanwhile a Revolutionary Court on Saturday charged a French woman, two Iranians working for the British and French embassies in Tehran and dozens of others with spying and assisting a Western plot to overthrow the system of clerical rule. Espionage and acting against national security are punishable by death under Iran's Islamic law.

French Foreign Minister Bernard Kouchner urged Iran to free the Frenchwoman, 24-year-old academic Clotilde Reiss, and rejected accusations against her of spying and helping a Western plot against Iran. "I want to clearly tell the Iranian authorities: these allegations are not true, Clotilde Reiss isn't guilty of anything," Mr Kouchner said on LCI television.

US national security adviser Jim Jones, speaking on American television, said the United States had urged Iran to release three American hikers who were detained there recently.

In order to calm widespread anger, Iran jailed the head of the Kahrizak detention centre after at least three people died in custody in the Tehran prison as the judiciary held trials of detainees arrested over post-election unrest.

Authorities say some 200 protesters remain imprisoned, including senior pro-reform politicians, journalists, activists and lawyers.

Leading moderates including Mr Mousavi and former president Khatami have called for the immediate release of detainees, saying their confessions were made under duress.