The wife of Iranian opposition candidate Mir Hossein Mousavi called for the immediate release of detained protesters as her husband was to appear at a mass protest outside the country's parliament.

In her statement, which appeared on Mousavi's Web site, Zahra Rahnavard said it was her "duty" to continue "legal" protests and condemned the presence of armed guards in the streets, Reuters reported.

"I regret the arrest of many politicians and people and want their immediate release," Rahnavard said in the Web site statement, according to Reuters.

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Rahnavard has raised eyebrows in Tehran for campaigning alongside her husband in the conservative state, and emerged as an important asset in her husband's campaign.

Meanwhile, Iran's supreme leader said Wednesday that the government won't give in to pressures over the disputed presidential election, effectively closing the door to compromise with the opposition.

"I had insisted and will insist on implementing the law on the election issue ... Neither the establishment nor the nation will yield to pressure at any cost," Supreme Leader Ayatollah Ali Khamenei said in a meeting with lawmakers.

Mousavi claims that hard-line President Mahmoud Ahmadinejad stole the June 12 presidential election through massive fraud. He has called for annulling the results and holding a new vote.

Iran also said it was considering downgrading ties with Britain, which it has accused of spying and fomenting days of unprecedented street protests over the vote.

Foreign Minister Manouchehr Mottaki was asked about the option of reducing diplomatic relations with London after a Cabinet meeting in Tehran.

"We are studying it," Mottaki said, according to state television.

Iran expelled two British diplomats Tuesday after bitterly accusing Britain of spying and fomenting days of unprecedented street protests over the vote.

The Associated Press contributed to this report.