Opposition leader Mirhossein Mousavi plans to attend weekly prayers in Tehran on Friday in his first official public appearance since a disputed vote that provoked mass protests by his pro-reform supporters last month, Reuters reported.
The sermon at Tehran University, which is broadcast live by state radio and can reach a huge audience, will be led by former President Akbar Hashemi Rafsanjani, a rival of re-elected President Mahmoud Ahmadinejad.
It takes place a day after Ahmadinejad accused Western powers of interfering in the June 12 election. He signaled a tougher foreign policy approach by his next government, due to take office in August.
Ahmadinejad also issued veiled criticism of Rafsanjani, a Mousavi supporter whom the hardline president enraged during a bitterly fought election campaign by accusing him of corruption.
"Nobody has the right to recognize special rights or incentives for himself or his relatives," Ahmadinejad said in a speech in the northeastern city of Mashhad on Thursday evening.
Rafsanjani, an influential cleric who was president in the 1990s, will lead the prayers after a two-month absence. Some of his relatives, including his daughter Faezeh, were arrested briefly for taking part in pro-Mousavi rallies.
June's election stirred the most striking display of internal dissent in Iran since the 1979 Islamic revolution and exposed deepening divisions in its establishment.
At least 20 people died in post-election violence. Mousavi and the authorities blame each other for the bloodshed. The security forces have managed to largely quell last month's street demonstrations, but Mousavi has remained defiant.
Anoush Ehteshami, an Iran expert at Britain's Durham University, said he did not expect a confrontation between Mousavi and Ahmadinejad supporters during the prayers, when worshippers usually gather both inside and outside the university.
"I don't think so. I think they will try and keep the lid on it," he said. "I doubt very much Ahmadinejad will be there. This is if you like the reformers' turn at Friday prayer."
Mousavi, Ahmadinejad's main moderate challenger in the vote, says it was rigged in the incumbent's favor. The president rejects the charge and has called it the world's "healthiest" election.
Supreme Leader Ayatollah Ali Khamenei has endorsed Ahmadinejad's victory, but Mousavi says the next government will be illegitimate.
The election also strained ties between Iran and the West, already at odds over Tehran's nuclear program. Western powers criticized the protest crackdown and Iran, the world's fifth-largest oil exporter, accused them of meddling.
On Tuesday, the pro-reform Etemad newspaper said Mousavi's reformist ally, former President Mohammad Khatami, would also attend the prayers.