TEHRAN (Reuters) - Iranian opposition leader Mirhossein Mousavi said on Friday he was ready to die for his reformist campaign after a disputed election in June, defying hardline calls for his execution.

A masked Iranian student, supporter of opposition leader Mirhossein Mousavi, gestures while holding a photo of the Islamic revolution's father, Ayatollah Ruhollah Khomeini, during a rally in central Tehran December 13, 2009. REUTERS/via Your View

“I’m not afraid of being one of the martyrs who lost their lives in their fight for their rightful demands since the vote,” Mousavi said on his website, five days after his nephew and seven other pro-reform protesters were killed during a rally.

Mousavi, whose allegation that the June presidential vote he lost to Mahmoud Ahmadinejad was rigged set off a wave of unrest, said in the statement the Islamic Republic was in “serious crisis.”

In his most outspoken remarks of recent months, Mousavi declared that “arresting or killing Mousavi, (or fellow opposition leader Mehdi) Karoubi ... will not calm the country.”

The remarks on his Kaleme website were a new challenge to the authorities, who have intensified their crackdown on the reform movement since last Sunday when eight people -- including a nephew of Mousavi’s -- were killed in protests on the day of the Shi’ite Muslim ritual of Ashura.

Hardliners have accused opposition leaders of igniting unrest, labeling them “mohareb” (enemies of God), a crime punishable by death under Iran’s Islamic law.

Such threats have apparently failed to silence Mousavi, who said he was ready to die for his cause.

“Such harsh remarks ... will create internal uprising ... My blood is not redder than that of other martyrs,” he said.

The anti-government protests, which have flared repeatedly since the election, have plunged Iran into the most serious internal crisis in the Islamic Republic’s 30-year history.

Mousavi supporters have defied government warnings against holding “illegal rallies,” using Muslim festivals and official days of commemoration as a cover for street gatherings.

Opposition leaders say the presidential vote was rigged to secure Ahmadinejad’s re-election. The country’s highest authority, Supreme Leader Ayatollah Ali Khamenei, said it was the healthiest in three decades.

Hardline cleric Ahmad Khatami criticized Mousavi’s statement, saying “he is repeating his past mistakes,” state radio reported.

NEW PHASE OF TURMOIL

The political turmoil has entered a new phase since Sunday, marked by bloody confrontations, arrests and hardline demands for stronger suppression of opponents of the government.

Cleric Ahmad Jannati, a staunch Ahmadinejad supporter, said on Friday the leaders of the “sedition” should be punished.

“I call on the judiciary to accelerate the legal procedure of those behind the recent unrest,” he told worshippers at Tehran University in a speech broadcast on state radio.

At least 24 pro-reform figures have been arrested, including three senior advisers to Mousavi, his brother-in-law and a sister of Iranian Nobel Peace Prize winner Shirin Ebadi.

“The country’s current situation is like a wild river and a hasty solution cannot calm down the situation,” Mousavi said, adding that the only way for the establishment to calm the unrest was to preserve the nation’s rights.

Mousavi, echoing reformists’ demand, called for “a change to Iran’s election law, an accountable government, the release of political prisoners and respect for press freedom.”

The authorities have accused Mousavi and Karoubi of links to “foreign enemies and anti-revolutionary groups” and vowed to show them no mercy unless they change course.

The clerical establishment has often accused foreign-backed forces of plotting to topple its leadership, which is locked in a dispute with the West over Iran’s nuclear work.

The police and Intelligence Ministry have warned Mousavi’s supporters they will face harsh treatment unless they halt their “illegal” rallies. Mousavi said the government was making a mistake by using force to end street protests.

“Let’s assume that you silence people by arrests, acts of violence and threats ... What solution do you have for the change in people’s view of the regime? How can you make up for the lack of legitimacy?” his statement said.

Opposition rallies have shown no sign of dying away. Police said they had arrested 500 protesters on Sunday and the opposition website Jaras said hundreds of protesters had been detained in Tehran and other cities since then.

Thousands of protesters have been arrested since the June election. Most have since been released but more than 80 have been sentenced to up to 15 years’ imprisonment and five have been sentenced to death.

The reformist opposition says more than 70 people were killed in violence that followed the June election. Officials say the death toll was half that and included Basij militiamen.

Jannati said “detained ‘rioters’ should be kept in jail as they will continue their devilish acts as soon as they are freed.”

Worshippers held a rally in Tehran on Friday, demanding that judiciary “take legal action” against opposition leaders, the semi-official Fars news agency reported.