A pro-reformist Web site says Iran has barred former President Mohammad Khatami from leaving the country.
The Web site Parlemannews says Mr. Khatami was scheduled to depart Thursday night to attend a nuclear disarmament conference in Japan.
There was no immediate reaction from the Iranian government.
Mr. Khatami was a key supporter of defeated presidential candidate Mir Hossein Mousavi in June elections. Opposition leaders claim that President Mahmoud Ahmadinejad stole the vote. The Iranian government has carried out violent crackdowns on anti-government protests staged since the presidential election.
Some information for this report was provided by AP, AFP and Reuters.