It was impossible to confirm the extent of the violence because of press restrictions on coverage of the post-election mayhem. But the witnesses reached by telephone said the confrontation, in the streets near the national Parliament building, was bloody, with police using live ammunition.

Defying Government warnings, hundreds, if not thousands of protesters, had attempted to gather in front of Parliament on Baharestan Square, witnesses said. They were met with riot police and paramilitary militia, who struck at them with truncheons, tear gas and guns. One witness said he saw a 19-year-old woman shot in the neck.

Some Opposition supporters said that Mir Hussein Moussavi had been scheduled to address the crowd, but initial reports indicated that he had not appeared.

The violence came as additional details emerged about the sweeping scale of arrests that have accompanied the nation’s worst political crisis since the 1979 revolution. A New York-based human rights group, International Campaign for Human Rights in Iran, listed the names Wednesday of 240 of the 645 people Iranian state media have reported detained in the crackdown. The total number of detained, the organisation said may be as high as 2,000.

Among them are people arrested in a Monday night raid of a campaign office for Moussavi in Tehran, Press TV reported on Wednesday. The Government said the office was being used as “a headquarters for psychological war against the country’s security”, and claimed that evidence had been found of “the role of foreign elements in planning post-election unrest”.

Earlier on Wednesday, Khamenei told legislators that he “insisted and will insist on implementing the law on the election issue”, according to accounts in the state-run media. “Neither the establishment nor the nation will yield to pressure at any cost.”

One of the three candidates complaining of poll irregularities, Mohsen Rezai, formally withdrew his complaints of vote-rigging, opening a rift among those who had challenged the poll outcome.

Rezai had complained that while the official count gave him 680,000 votes, he had evidence that 900,000 people voted for him.

On Wednesday, Press TV reported, he decided to abandon the complaint, saying the current “political, social and security situation has entered a sensitive and decisive phase which is more important than the election”. Rezai was quoted as calling the ballot a “clear sample of religious democracy”.

Iran’s Foreign Minister, Manouchehr Mottaki, said on Wednesday Tehran was reviewing whether to downgrade ties with Britain, which Iran has accused of interference in its disputed presidential election, the ISNA semi-official news agency said.