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.

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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."

Mr Makhmalbaf, a friend of Mr Mousavi for 20 years, said that there were reports from Iran that some of the militia deployed to suppress protest were "speaking Arabic". "That is unconfirmed but it suggests that the regime is unable to trust its own security forces to repress the Iranian people," he said. "It suggests that people are being used from abroad."

Mr Makhmalbaf is touring Europe to try to explain events in Iran to the media. He denied reports that he had been formally appointed as a spokesman for Mr Mousavi outside Iran. "I am simply speaking on behalf of all the people who are protesting and dying on the streets of Iran," he said.

Mr Mousasvi's means of communication had been cut off, or confiscated, just after the disputed election, Mr Makhmalbaf said. He had therefore been asked informally to make sure that a true picture of what was happening in Iran reached the outside world.

Asked to explain where the protests might go from here, he said that Mr Mousavi had urged his supporters not to confront the regime directly but to "adopt the tactics of Gandhi, the tactics of non-violent protest and civil disobedience".

"The problem is that the more people that are killed, the more angry people will be, the more protesters will want to come out onto the streets."

The film director dismissed all hope of some form of negotiated agreement. "Within the last ten days, there has been a meeting between Mousavi and Ayatollah Khamanei," he said. "Nothing came of this meeting. I do not know of any further dialogue which is now going on."

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Asked to explain how a Mousavi-run Iran would differ from an Ahmadinejad-run Iran, Mr Makhmalbaf said: "The first thing to say is that it is now clear that Ahmadinejad is irrelevant. He is not the real power."

If Mousavi was to become president, he said, Iran would invest in "improving the economy for ordinary people, not creating nuclear weapons or supporting conflicts abroad". Secondly, he said, there would be an end to the "constant harassment of young people which means that virtually every young person in Iran has been beaten up by the security forces."