Iran has released on bail a grandson of former President Akbar Hashemi Rafsanjani after he expressed "regret" for taking part in post-election protests, an Iranian news agency reported on Tuesday.

Hassan Lahouti was detained by security police on Sunday at Tehran airport after arriving on a flight from abroad.

"After some investigations and after he expressed regret over his actions, he was released from prison on bail," Tehran prosecutor Abbas Jafari Dolatabadi was quoted as saying by the semi-official Fars news agency.

Lahouti's grandfather, who heads the powerful Assembly of Experts, is still a powerful player in the ruling establishment.

A source close to the family had told Fars that Lahouti, believed to be in his 20s, left the country last year days after the presidential vote in which President Mahmoud Ahmadinejad was re-elected.

The disputed June poll plunged Iran into its worst unrest since the 1979 Islamic revolution. Authorities deny allegations of vote-rigging.

Thousands of people protesting against the conduct of the election were arrested after the vote. Most have since been released, though more than 80 people have received jail sentences of up to 15 years.

Lahouti's mother, Faezeh Hashemi, was among several of Rafsanjani's relatives held briefly for joining rallies in June, when the unrest first erupted.

Reuters