Iranian authorities opened the registration process on Tuesday for candidates in the June 14 presidential vote that will pick a successor to President Mahmoud Ahmadinejad.

The Interior Ministry opened the five-day registration process at 8 am, according to media reports, with a string of conservative hopefuls in the running but key reformists yet to come forward.

Interior Minister Mostafa Mohammad Najjar advised hopefuls against waiting until the last minute to register, while warning against early campaigning, the state broadcaster's website reported.

The polls will be followed closely by the international community four years after the government suppressed a wave of demonstrations that erupted when Ahmadinejad secured a second term.

Under the constitution, the outgoing president cannot stand for a third consecutive term.

His successor is expected to face an array of challenges, including Iran's worsening economy targeted by international sanctions over the country's nuclear program.

Joining the race

On Tuesday, former nuclear negotiator and moderate figure Hassan Rowhani joined the race with a promise to "save the economy and (engage) in constructive interaction with the world," ISNA news agency said.

On Iran's nuclear issue, Rowhani said he will try to return the country's nuclear dossier from the UN Security Council to its "real place", the International Atomic Energy Agency. Iran's nuclear program is peaceful and the issue should be settled in the IAEA, he said.

As Iran's chief nuclear negotiator from 2003 to 2005 in reformist president Mohammad Khatami's time, Rowhani led the country's nuclear negotiations with the European Union trio of Britain, France and Germany.

Many conservative hopefuls have expressed readiness to stand for election.

Among them are heavyweights Ali Akbar Velayati - foreign minister from 1981 to 1997 and current foreign affairs adviser to Supreme Leader Ali Khamenei - and Mohammad Baqer Qalibaf, a former national police chief who is now mayor of Tehran.

The process of screening candidates is entrusted to the Guardians Council, an unelected body controlled by religious conservatives appointed by Khamenei, who has the final say on all key issues.

The council is set to announce the names of those who have been cleared to stand no later than May 23.

Ahmadinejad is widely expected to tap his close aide and former chief of staff, Esfandiar Rahim Mashaie, to run for office. But Mashaie has yet to announce intentions to register.

The vetting process by the Guardians Council is based on articles of the constitution, which call for candidates to have a political and religious background, and to believe in the principles of the Islamic republic and its official religion.

Any contender must be at least 18, but an upper age limit has not been specified.

Candidates who pass the council's screening will have three weeks to campaign ahead of the election.

In 2009, 475 Iranians registered as prospective candidates but only four were cleared to run, including Mohsen Rezaei, a former commander of the Revolutionary Guards, who is expected to stand again.

AFP-AP-Xinhua