Iranian opposition leader Mehdi "Karoubi has been released temporarily, he and his wife are looking for a new house," the conservative website Jahan said on Saturday. "In the new house they would still be under the supervision of the security forces to not commit any act against national security."

Opposition websites also carried the news, quoting a Karoubi advisor who had told the BBC's Farsi service that the Karoubis needed to move as the tight security around their Tehran home had meant their neighbours had had to move out.

The 73-year-old cleric stood for election against President Mahmoud Ahmadinejad in June 2009. Along with fellow reformist candidate Mirhossein Mousavi, he became a figurehead of the post-election protests by Iranians who believed the vote was rigged to secure the re-election of the hardline incumbent.

The government denied any vote rigging and said the protests were stirred up by Iran's foreign enemies who aimed to overthrow the country's Islamic form of government.

Both Karoubi and Mousavi have been held incommunicado since they called their supporters onto the streets for a Feb.14 rally in support of uprisings in the Arab world -- the first demonstrations by their "Green movement" since street protests were crushed by security forces at the end of 2009.

Members of the conservative dominated parliament have called for them to be tried and hanged but so far authorities have chosen to isolate rather than officially arrest them, wary of angering their supporters.