Lawyer Masoud Shafii who represented the now free US hikers held for two years in Iran on espionage and illegal entry charges was barred from leaving the country on Sunday, a source close to the case told AFP.
"This morning at around six o'clock (0230 GMT), after getting his passport stamped and as he was boarding the plane, his passport was confiscated by order of the judiciary," the source said on condition of anonymity.
The source added that Shafii "could not proceed to his final destination which was the United States," without elaborating on why his passport had been seized.
On Tuesday Shafii was arrested at his home and questioned for several hours by judiciary officials before being released, the source said, adding that agents confiscated documents, his computer and his passport, but returned them later.
Shafii represented Shane Bauer, Josh Fattal and Sarah Shourd in a case which lasted for more than two years. He always maintained that his clients were innocent, and was criticised by conservative hardliners in the Islamic republic.
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Shafii also criticised the judiciary for not allowing him proper access to the three, as required by the law.
He met them briefly only three times in two years, once before the start of their trial, and once before each of two hearings in February and August.
Bauer, Fattal and Shourd were charged with illegal entry and spying on Iran after they were arrested in July 2009 along the unmarked Iran-Iraq border.
Shourd was released on bail in September 2010 on health grounds, and her two companions were freed on bail on September 21 after being sentenced in August to eight years in prison each by a Tehran revolutionary court.
Four days later Fattal and Bauer accused Iran at a New York news conference of using them as hostages in its power struggle with the West, and described hearing the anguished cries of fellow inmates being beaten in Tehran's Evin prison.
Iran's judiciary promptly denied their charges.
The hikers case angered Washington, already mired in deep differences with Tehran over its controversial nuclear programme, its refusal to recognise Israel and its support for militant groups in the Middle East.