The Iranian opposition leader Mirhossein Mousavi is under 24-hour guard by secret police and no longer able to speak freely to supporters, according to the film director Mohsen Makhmalbaf.

Mr Makhmalbaf, 52, an informal spokesman abroad for the protest in Iran, said that Mr Mousavi was not under arrest but “he has security agents, secret police with him all the time. He has to be careful what he says.”

In a telephone interview, Mr Makhmalbaf, the director of the 2001 film Kandaha, denied suggestions that the protests against the re-election of President Mahmoud Ahmadinejad were losing steam.

“The regime, arguably, is losing ground, not the protests,” he said. “Ordinary Iranians are openly rejecting the legitimacy and power of Ayatollah Khamanei. That is entirely new, unheard of.”