Iranian reformist leaders Mir Hossein Moussavi and Mehdi Karouobi are reported to have left Tehran.
The circumstances of their departure remain shrouded in mystery.
The official IRNA news agency says they have fled voluntarily to the north of the country after seeing a “surge of anger from people who desire to punish”.
But an opposition website claims the pair have been forcibly removed from the capital by members of the Revolutionary Guard and Intelligence Ministry officials.
They are said to have been taken to the city of Kelar Abad.
As pro-government rallies take place in Iran, opposition supporters are being warned to give up their plans for further protest.
The country’s police chief has told the opposition to expect what he called harsh treatment if they try to demonstrate.
The clerical leadership is attempting to reimpose strict rule after clashes over the weekend left at least eight people dead. Numerous opposition figures have been detained.
In the face of international criticism, President Mahmoud Ahmadinejad has denounced the anti-government demonstrations as a “foreign-backed, nauseating masquerade”.
A spokesman for Supreme leader Ayatollah Ali Khamenei has described opposition leaders as “enemies of God” who should be executed.
Despite restrictions on the foreign media, the internet and mobile phone services, amateur video footage of the violence continues to emerge.
The reformist opposition is vowing to hold further demonstrations, saying crackdowns are only making their resolve stronger.