Government loyalists held a rally on Friday, calling for the execution of Mousavi and Karroubi [AFP]

Mehdi Karroubi, the Iranian opposition leader, has asked to be put on trial in public, his website reported.

Sahamnews.org said on Sunday that Karroubi made the call in a letter to Ayatollah Sadegh Larijani, Iran's judiciary chief, that was posted on the website as he was under  "complete house arrest" and unable to deliver it.

"I have a request to you that as soon as possible and through legal channels ... a public court be set up so the indictment and defence are heard," Karroubi said in the letter, according to Sahamnews.org.

"It should be a fair and public court so the people get to know the truth," he said, stressing that his "firmness in defending the legitimate right of the people was unshakable".

The letter was posted on a day of nationwide anti-government rallies called for by a group supporting Karroubi and fellow opposition leader Mir Hossein Mousavi.

The call from the Council for Coordination of the Green Movement Hope was posted on Sahamnews.org and Mousavi's website, Kaleme.com, on Thursday, prompting a warning from authorities for protesters to stay off the streets.

Sunday's rallies were to commemorate two deaths last Monday when security forces clashed with opposition supporters, the group said. 

Following Monday's demonstrations, some members of the Iranian parliament called for the Karroubi and Mousavi to be hanged.

Iran's state media reported that security forces were prepared to forcefully confront protesters, and social media site Twitter and Facebook carried messages indicating that heavy uniformed and plainclothes security personnel were in place in Tehran's Enghelab Square.

Karroubi and Mousavi, once pillars of the Islamic regime, have rebelled against the establishment since their rival, Mahmoud Ahmadinejad, was re-elected in the 2009 presidential poll.