Iran on Satuday marks one year since a disputed presidential election returned hardline Mahmoud Ahmadinejad to power, with his rivals uncompromising in their continued opposition to his rule.
However, opposition leaders Mir Hossein Mousavi and Mehdi Karroubi have called off plans to stage fresh anti-government demonstrations over safety concerns as the authorities vowed to crack down on any new protests.
The security forces used deadly force to quell the massive street demonstrations that erupted after the results of the June 12 vote last year -- a poll which the opposition charged had been massively rigged.
Street protests against Ahmadinejad have not now been held for months, and Tehran's hardline governor renewed warnings yesterday against any attempts to demonstrate today.
"Any illegal move to disrupt public order and trouble people will not be tolerated and will be dealt with," Morteza Tamaddon was quoted as saying by the state news agency IRNA.
Ahmadinejad's re-election bitterly divided Iran's political elite, and the regime's subsequent crackdown on protesters drew a torrent of international condemnation.
The authorities, led by supreme leader Ayatollah Ali Khamenei, blamed the unrest on Western powers, accusing them of masterminding the protests in a bid to topple the Islamic regime.
But former premier Mousavi and ex-parliament speaker Karroubi, who were close to Iran's revolutionary father Ayatollah Ruhollah Khomeini, brush aside such allegations.
For them, the opposition "Green Movement" is a grassroots initiative pursuing the aspirations of Iran's 1979 revolution, including free elections, freedom of expression and respect for human rights.
Late yesterday, Mousavi said on opposition website Rahesabz that the current rule has distanced itself from the intial goals of revolution and the constitution and is now "shutting peoples' mouths, curbing the media and holding elections as we saw last year and filling the prisons."
US President Barack Obama, whose country has had no diplomatic ties with the Islamic republic for three decades, urged the world to support the Iranian people in their fight for "freedom."
"The courage of the Iranian people stands as an example to us and it challenges us to continue our efforts to bend the arch of history in the direction of justice," Obama said in a statement.