Hundreds of opposition supporters have been arrested and tried in the fierce crackdown that crushed opposition protests in the wake of the election, which the opposition claimed President Mahmoud Ahmadinejad won by fraud.

So far, authorities have stopped short of trying to jail the reform movement's top leaders — Mir Hossein Mousavi, who claims to have been the real victor in the election, fellow candidate Mahdi Karoubi and former President Mohammad Khatami — apparently out of concern it could spark a new wave of protests and fuel the opposition.

But a series of recent public warnings by hard-liners that they could be tried may be a sign that Iran's leadership believes the opposition has now been sufficiently suppressed to respond to their arrest.

On Friday, Tehran prosecutor Abbas Jafari Dowlatabadi told worshippers at Tehran University that the opposition leaders are criminals who sought to topple the current system of governance through street protests.

"We've said many times ... that leaders of sedition are criminals and charges against them will be investigated. That they will stand trial is definite," Dowlatabadi said in his address, broadcast live on state radio.

"They (opposition leaders) undermined public trust in the system ... and disrupted security in the country. Heavy punishment awaits them," Dowlatabadi said. "But since their backing is connected to the dirty hands of the US and the Zionists, we need to handle the case with more care." The repeated warnings may have a double aim — to discredit the opposition leaders as criminals in the eyes of the public and to test the waters to see if their arrest would prompt a new wave of protests. Mousavi, Karoubi and Khatami are already barred from leaving the country. Though no travel ban had been officially announced, Khatami was forbidden to travel to Japan in April to attend a conference on dialogue between cultures.

Mousavi and Karoubi said earlier this month that they are already living in a "big prison" and did not care if they were put behind bars in a "small prison" for defending the trampled rights of the Iranian nation.

Mousavi recently likened Iran's ruling system to a North Korean style dictatorship with a few cosmetic democratic gestures and criticized the disputed June 2009 election as a coup against democracy.

Last week, State Prosecutor Gholam Hossein Mohseni Ejehi indicated that the country's political leadership is debating whether to arrest the three, pointing to "considerations ... at the top level." "There are considerations about arresting the sedition leaders," Ejehi told reporters. "Rest assured that should these considerations clear it, we won't postpone their arrest until tomorrow. I would order the Tehran prosecutor to arrest them before sunset."

Many other opposition figures who have been convicted were tried on charges of being "mohareb," or "fighting against God." The elite Revolutionary Guards, Iran's most powerful military force which also holds considerable political power, has pushed for the three opposition leaders to be tried on the same charges.