Iranian President Mahmoud Ahmadinejad has called off a trip to Libya for an African Union summit.

A spokesman for Mr Ahmadinejad confirmed that the visit had been cancelled without giving a reason.

It would have been the president's second foray abroad since the disputed 12 June election set off Iran's most significant internal unrest since the 1979 Islamic revolution.

In a show of confidence, Mr Ahmadinejad had attended a regional summit in Russia four days after the vote, ignoring huge street protests by supporters of losing candidates Mir-Hossein Mousavi and Mehdi Karoubi, who both claim the election was rigged.

Iran's Guardian Council has since endorsed the election result and dismissed complaints of irregularities, saying a partial recount had shown these were baseless.

But Mr Karoubi, a reformist cleric who came fourth in the poll, has remained defiant, saying that he viewed Ahmadinejad's government as illegitimate.

Both Mr Karoubi and Mr Mousavi, a moderate former prime minister, have called for the election to be annulled.

Opposition supporters continue to reject the election result in what amounts to an unprecedented challenge to Supreme Leader Ayatollah Ali Khamenei, who has upheld the outcome.

Mehdi Karoubi, a white-bearded cleric who was close to Iran's revolutionary leader Ayatollah Ruhollah Khomeini, has also demanded the release of 'thousands' of people arrested during the unrest.

Police have said that only 1,032 people were arrested during the protests, and say most have since been released.

Iran has accused foreign powers, notably Britain and the US, of fomenting the post-election demonstrations.