"The end of the apartheid regime in South Africa, of military juntas in South America, of the former Soviet Union -- all of it came at the hands of the people of those nations themselves," Reza Pahlavi told the Daily Telegraph.

"None of this could have happened without foreign support, but that is not the same as an occupying army that comes in and changes a regime -- I don't see how that can ever be legitimate."

The son of the late shah added: "Change must come to Iran by civil disobedience and non-violence, I stress that. We can't have change at any cost... what happens must be the will of the people."

Pahlavi left Iran a year before his father, shah Mohammad Reza, was ousted in the 1979 Islamic revolution, and has lived in the United States since 1984.

As more protests were held this week on the streets of Tehran, he told the Telegraph that "the ingredients for change have reached almost boiling point, despite the attempts of the regime to crack down".

And he argued that internal pressure was the only kind that would work on President Mahmoud Ahmadinejad over Iran's nuclear programme, which Western powers fear is aimed at creating nuclear weapons, something Tehran denies.

"The threat from their own people is the only leverage that will matter, on the nuclear issue especially, much more so than endless rounds of failing diplomacy," Pahlavi said.

However, he said the international community must show their support for the protesters challenging Ahmadinejad's regime.

"If they are holding up signs in English on the streets of Tehran it is not to practice their language skills, it is obviously meant for the outside world," he said.

If this support is not forthcoming, "we may as well run up the white flag on the nuclear threat. We have a window of opportunity", he said, adding that for people in Israel this was a "matter of life and death".

He said that if UN sanctions could not be agreed, multilateral penalties should be imposed, adding: "We need smart sanctions to weaken the regime and its apparatus" without harming the people of Iran.

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