Iranian election authorities say several high-profile politicians, including reformists and allies of Mahmoud Ahmadinejad, the outgoing president, have registered for presidential elections to be held on June 14.
Mohammad Bagher Qalibaf, Tehran's mayor, Ali Akbar Javanfekr, an Ahmadinejad adviser, and Davood Ahmadinejad, the president's elder brother, are among hundreds who have joined the race ahead of Saturday's registration deadline.
Former president Akbar Hashemi Rafsanjani has also registered himself as a candidate.
Rafsanjani, 78, is expected to draw support from reformists because he backed the opposition movement whose protesters were crushed after the last disputed election in 2009.
"He [Rafsanjani] wields enormous political clout in this country," Al Jazeera's Soraya Lennie, reporting from Tehran, said.
"He is a pragmatist. He sometimes flip-flops between the conservative camp and reformist camp, depending on who he is supporting.
"He favours economic reforms, revitalising Iran's economy and fixing it after the Iran-Iraq war in the 1980s. But he also favours better relations with the US, with Arab countries and the rest of the world."
Iran's chief nuclear negotiator Saeed Jalili and pro-reform activists Ebrahim Asgharzadeh and Javad Eta'at have also signed up.
The campaign is taking shape as open season on Ahmadinejad's legacy and his combative style that bolstered his stature among supporters but alarmed critics.
Ahmadinejad is barred by law from seeking a third term due to term limits under Iran's constitution.
The Guardian Council, a constitutionally-mandated 12-member council, will vet the applicants before allowing them to run.
The poll will be the first presidential election since 2009, when mass protests dubbed the "Green Movement" erupted after the disputed re-election of Ahmadinejad over reformist candidates Mir Hossein Mousavi and Mehdi Karoubi.
Since then, reformists who espouse greater social and political freedoms have been suppressed or sidelined. Mousavi, his wife, and Karoubi have been under house arrest for more than two years.
The prestige of Iran's most powerful man, Supreme Leader Ayatollah Ali Khamenei, now appears threatened by intense rivalry between groups polarised by Ahmadinejad, who has been accused of wanting to erode the system of clerical rule.
About 600 candidates have registered so far, including moderate cleric Hassan Rohani, a former nuclear negotiator under reformist president Mohammad Khatami, and several other reformists, including former member of parliament Mostafa Kavakebian and Mohammad Aref, a vice president under Khatami.
Qalibaf, the charismatic mayor of Tehran and a member of a three-man coalition of "Principlists" - loyal supporter of Khamenei and the theocratic system - is, by implication, hostile to Ahmadinejad.
Two other Principlists, Mohammad Hassan Abu-Torabi Fard and former health minister Kamran Baqeri Lankarani, are also running, as is Mohsen Rezaie, who headed the Revolutionary Guards and lost to Ahmadinejad in 2009.