The hundreds of hopefuls who put their names forward in recent days will be vetted by the Guardian Council, controlled by Iran's supreme leader, Ayatollah Ali Khamenei. Michael Theodoulou reports
Rafsanjani enters Iran's presidential election at the last minute
Two of Iran's most high-profile contenders for president registered yesterday at the last minute to replace Mahmoud Ahmadinejad, who is constitutionally bound to step down after the June 14 vote.
Ayatollah Ali Akbar Rafsanjani, 78, a founding father of the Islamic republic and two-time president who advocates better relations with the West and the Arab world, registered just before the deadline. He is a bitter critic of the outgoing president and considered a master of realpolitik rather than an ideologue.
Mr Ahmadinejad's most controversial ally, Esfandiar Rahim Mashaie, also registered at the 11th hour . He is vilified by Iran's ruling old guard for putting Iranian nationalism above Islam.
The hundreds of hopefuls who put their names forward in recent days - many of them long shots and a dozen women - will be vetted by the Guardian Council, a panel of six clerics and six jurists controlled by Iran's supreme leader, Ayatollah Ali Khamenei. Candidates are required to have a political and religious background and to believe in the principles of the Islamic republic.
Only a handful will make it on to the final ballot, to be announced on May 23, leaving just three weeks for campaigning before the vote.
Ayatollah Khamenei, who has held power for 24, years, is keen to ensure there is no repetition of the huge street protests that swept Iran four years ago after Mr Ahmadinejad re-election which reformists insisted was rigged.
The ayatollah also wants an end to the highly damaging public feuding between the outgoing president's allies and fellow hardliners which marked Mr Ahmadinejad's second four-year term.
The vote comes at a critical time for the Iranian regime, which is struggling under choking western sanctions imposed over its nuclear programme, and under international and regional pressure because of its support for Bashar Al Assad's regime in Syria.
Ayatollah Khamenei once championed the outgoing president but now wants him to have no more influence when he steps down this summer. Mr Ahmadinejad has repeatedly challenged the supreme leader's authority.
Reformist groups have been ruthlessly suppressed since 2009 and the next president is likely to be picked from among a handful of politicians known for their loyalty to Mr Khamenei.
The ayatollah's interests in the election are represented by a trio of high-profile acolytes. One is Gholam Ali Haddad Adel, 67, a former speaker of parliament whose daughter is married to Mr Khamenei's son, Mojtaba.
The second is Ali Akbar Velayati, also 67, who has served as the supreme leader's chief foreign policy adviser for 16 years. He is a doctor by training who studied infectious diseases at John Hopkins University in the United States.
The third, and by far the most charismatic, is Tehran's suave mayor and Iran's former national police chief, Mohammad Baqer Qalibaf, 52, a former Revolutionary Guard commander and pilot.
The president's conservative opponents have attacked Mr Ahmadinejad's legacy, blaming him for Iran's economic woes - the main concern of voters - and accusing him of recklessly antagonising the West with inflammatory rhetoric.
Mr Qalibaf recently took the president to task for denying the Holocaust. "We were never against Judaism. It's a religion," he said last month. "No one could accuse us of being anti-Semitic. But suddenly, without consideration for the results and implications, the issue of the Holocaust was raised. How did this benefit Iran or the Palestinians?"
Iran's dour chief nuclear negotiator, Saeed Jalili, 47, also threw his hat into the ring yesterday. He commands respect among Iran's hardliners and lost his right leg fighting with the Revolutionary Guards on the front-line against Iraqi forces in the 1980s.