Tensions flared in Tehran Wednesday night as thousands of protesters marched to the state television center, enraged by the discovery that President Mahmoud Ahmadinejad was being given more airtime than his opponents.

The demonstration came as a leading conservative accused reformists of fomenting a "velvet revolution." Yadollah Javani, a leader of the hardline Revolutionary Guards, said that reformists were going to claim vote-rigging if their candidate, Mir Hossein Mousavi, loses in Friday's presidential elections. He vowed to crush any post-election violence.

As the accusations flew, Hojatoleslam Ali Akbar Hashemi Rafsanjani, a former president and powerful cleric, wrote an open letter to Ayatollah Ali Khamenei, Iran’s Supreme Leader, complaining about allegations of corruption that Ahmadinejad had levelled against his family in a televised debate last week. He warned that Khamenei’s failure to act against those "lies" could spark social unrest.

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"Even if I keep quiet, part of the people, groups and parties will undoubtedly not bear this situation any more and set off social upheavals," said Hojatoleslam Rafsanjani, who is backing Mousavi.

In another remarkable intervention, about 50 clerics from Qom, Iran’s religious nerve-center, also rebuked Ahmadinejad, stating in an open letter that "accusing people in a session when they are not present is contrary to sharia." Such conduct would "spread disappointment among the people and make our enemies happy."

These developments expose deep splits within a ruling establishment that never normally airs its disagreements in public and come on the eve of a landmark election in which Mousavi, a relative moderate, could become the first challenger to defeat an incumbent president in the Islamic Republic’s 30-year history.

There are no reliable opinion polls in Iran, but Mousavi has visibly gained momentum in recent days and his exuberant supporters have flooded on to the streets of Tehran in huge numbers. The usual restrictions on dissent have been largely swept aside as the regime has loosened — or lost — its grip ahead of the election.

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