He denied sending a "coded" message of support to the opposition in Tehran in a greeting sent out to mark the Norouz festival marking Iran's new year.

In it he expressed hope that the Iranian people "will be able to enjoy a year that fulfils their hopes and ambitions and allows them to express freely their own aspirations for the future".

Observers said the message would be seen by Tehran - which blames the UK and other western countries for fomenting dissent - as a "coded" message of support to its opponents.

But Mr Miliband has been a regular critic of the suppression of protests in the wake of last year's disputed presidential election and he said there was "nothing coded" about his words.

"What I am saying is that the Iranian people should be able to demonstrate, to express their views in an open way without fearing being beaten, imprisoned, shot in the streets or, is some cases, executed in show trials," he told BBC Radio 4's Today.

"This is not about the British Government trying to choose the government of Iran - that is a matter for the Iranian people. What I think is a legitimate matter of international concern is that Iranians are not able at the moment to assert their very basic human rights not are they able to listen to international media.

"So this is an Iranian regime quite nervous, you might say paranoid, about its future and it is denying basic rights to its people. I think it is right that we speak out about that."

The UK did not oppose the regime per se, he said, adding: "we do not like the policies they are pursuing."

Mr Miliband backed a renewed offer of diplomatic dialogue made by US President Barack Obama in an online video message released to coincide with the new year celebrations.