In late January, a former deputy of conservative ex-president Mahmoud Ahmadinejad jailed for embezzlement raised explosive allegations that have now spurred speculation that Ahmadinejad himself could face charges.

They were made in a private letter that was published by the Iranian Labour News Agency, giving a rare insight into splits at the top at a time when the former president, a fierce critic of the West, was showing signs of preparing a political comeback.

Ahmadinejad has denied the allegations, which linked him to the case, and his supporters say they are politically motivated.