Tuesday's U-turn was made in response to a demand from supreme leader Ayat Allah Ali Khamenei amid fears that the disqualification of reformers would prompt voters to boycott the poll and present the 26-year-old Islamic government with a crisis of legitimacy, state media reported.

The head of the Guardians Council, Ayat Allah Ahmad Janati, was quoted as writing to Khamenei that "as you consider it desirable that all people in the country from different interests have the opportunity to take part ... the competence of Mr Moin and Mr Mehr-Alizadeh is recognised".

Moin was the candidate chosen by the main reformist party, the Islamic Iran Participation Front (IIPF), and seen as the only credible pro-reform figure trying to run for president.

Mehr-Alizadeh is currently a vice-president in Khatami's cabinet, and was running as an independent.