Iran's opposition leader on Wednesday denounced the country's ruling system for being 'totalitarian' like the old Nazi and Soviet regimes, with lying to its people being its defining characteristic.

Mir Hossein Mousavi statement comes as reaction to a stepped up campaign by the ruling system to discredit opposition leaders, calling them traitors that would ultimately be prosecuted.

Open gallery view Mir Hossein Mousavi Credit: AP Photo / Ben Curtis

"They are resorting to methods (against the opposition) used in totalitarian regimes like Stalin in the Soviet era or (former dictator Nicolae) Ceausescu in Romania," Mousavi said in a statement posted on his website.

He added that the propaganda statements of Joseph Goebbels in Nazi Germany paled in significance to the lying done by Iran's rulers.

"They've surpassed Goebbels in telling lies. Leveling accusations and telling lies is part of their ossified faith," he said.

Tehran's chief prosecutor, Abbas Jafari Dowlatabadi, said last month that it was only a matter of time before opposition leaders are put on trial for the unrest following the disputed 2009 presidential election.

Mousavi and Mahdi Karroubi - who both ran in the disputed 2009 presidential elections - as well as former reformist President Mohammad Khatami are already banned from leaving the country.

So far, however, authorities have stopped short of trying to jail the reform movement's top leaders, possibly 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 Islamic clerical leadership believes the opposition has been sufficiently suppressed that their arrest would not spark a significant backlash.

Mousavi and Karroubi said last month that they are already living in a "big prison" and didn't care if they were put behind bars in a "smaller" 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.

The opposition claims that Mousavi was the rightful winner of the 2009 election and that hard-line President Mahmoud Ahmadinejad was declared the winner through massive vote fraud.

Hundreds of thousands of opposition supporters took to the streets in the aftermath of the election in support of Mousavi but their peaceful protest was crushed by security forces.

The opposition says more than 80 demonstrators were killed in the turmoil. The government, which puts the number of confirmed deaths at 30, accuses opposition leaders of being "stooges of the West" and of seeking to topple the ruling system through street protests.