TEHRAN - Iranian opposition leaders called on Tuesday for the immediate release of hundreds of people arrested in a crackdown on post-election protests and denounced the "brutal attacks" by security forces.

The call was issued by defeated presidential candidates Mir Hossein Mousavi and Mehdi Karroubi and former president Mohammad Khatami, as the opposition remained defiant over the disputed re-election of Mahmoud Ahmadinejad.

"The useless wave of arrests should end immediately and those who are being detained without even committing the slightest sin should be released," they said in a joint statement on Mousavi's campaign website, Ghalamnews.

Iran was rocked by violent street protests after the June 12 vote, with authorities rounding up reformists, political activists, journalists and protestors to quell the worst unrest since the 1979 Islamic revolution.

The repression triggered global outrage against Tehran, but Iran lashed out at the West, blaming Britain in particular for stoking violence which the authorities say left 20 people dead.

The opposition leaders also denounced what they called "brutal attacks" on "innocent people, student dormitories and residential houses" by Iranian security forces.

"The atmosphere where security forces continue to be deployed must end, as it only radicalises political movements," their statement said.

"If rights of the the protesters had been respected or if the people had not been lied to or disrespected, the situation would have never turned into a national crisis."

The post-election turmoil shook the very pillars of the Islamic regime, exposing deep differences in the country of 70 million people and even saw unprecedented criticism of supreme leader Ayatollah Ali Khamenei.

Iran's police chief Esmail Ahmadi Moghadam said last week that "two-thirds" of the some 1,000 people arrested during the protests have been released. Human rights groups estimated that as many as 2,000 had been detained.

Mousavi has branded the election a "shameful fraud" and continues to call for a fresh poll despite the powerful electoral watchdog, the Guardians Council, upholding Ahmadinejad's victory.

Khamenei, who has also given his staunch backing to the hardliner's re-election for another four years, on Monday warned Western countries against meddling in Iran.

"The Iranian nation warns the leaders of those countries trying to take advantage of the situation, beware! The Iranian nation will react."

Iran continues to hold one of nine local British embassy employees arrested on accusations of inciting violence, while Paris said the authorities have detained a French woman academic in Tehran’s notorious Evin prison.

President Nicolas Sarkozy said on Tuesday that spying charges against Clotilde Reiss, 23, were "pure fantasy" and that she should be released "very, very soon."

Iranian authorities have made no comment on her detention.

In Vienna, former Iranian president Abolhassan Banisadr boldly accused Khamenei -- who has ruled the Islamic republic for 20 years -- of being personally behind the alleged election irregularities.

"Khamenei ordered the fraud in the presidential election and the ensuing crackdown on protestors," Banisadr said at a symposium.

"The regime is edging closer to the abyss and is holding on to power solely by means of violence and terror," said Banisadr, who was Iran's first elected post-revolution president and has been living in exile in France since 1981.

US President Barack Obama, who had criticised the Iranian crackdown and raised questions about the election, strongly denied that the United States had given Israel a green light to strike Iran's nuclear facilities.

Obama said in an interview with CNN that diplomatic channels should be used to resolve the international standoff over Iran's nuclear drive which the West fears is a cover for efforts to build atomic weapons despite Tehran's denials.