Ali Akbar Hashemi Rafsanjani to stand for Iran presidency
Iranian ex-President Ali Akbar Hashemi Rafsanjani has registered for June's presidential election, a few minutes before an official deadline.
Correspondents say Mr Rafsanjani, 78, is virtually assured the support of reformers and could pose a real challenge to the country's conservative leadership.
Constitutionally, President Mahmoud Ahmadinejad cannot stand again.
But his choice of candidate registered minutes before Mr Rafsanjani.
Hardline nationalist Esfandiar Rahim-Mashaei, a close friend of Mr Ahmadinejad, is also seen as a threat to the clerical elite around Supreme Leader Ayatollah Ali Khamenei.
Iran's chief nuclear negotiator, Saeed Jalili, has also registered. He is seen as close to Ayatollah Khamenei.
More than 400 candidates in total have registered but Iran's Guardian Council - a body controlled by the supreme leader - decides who can stand.
The results of the last presidential elections, in 2009, were disputed by the reformist opposition, triggering mass street protests.
The return of the seasoned centrist politician to frontline politics is seen as a serious challenge by the conservative-dominated establishment.
Mr Rafsanjani, 78, has already served as the country's president, parliamentary speaker and the head of the Assembly of Experts which appoints, and theoretically has the authority to dismiss, the supreme leader.
Conservatives are unhappy that Mr Rafsanjani has, for the past four years, expressed support for the pro-reform movement. He has called for the release of political prisoners and greater political freedoms for parties prepared to work within the existing constitution.
However, those who seek to change the regime by gradual reforms see Mr Rafsanjani as the master manipulator who has a foot in the door of the establishment and a hand in the affairs of the opposition, and who could, theoretically, create a more open and predictable political climate.
Seen as a moderate, Mr Rafsanjani is expected to gain support from reformers after supporting the protests.
Opinion polls suggest he is currently the most popular of the candidates.'Lack of trust'
The former president put his name forward in the last half hour before nominations closed.
His aides said he was waiting to see whether Iran's supreme leader would have any objections to his running as a candidate.
"I came to serve. It is the right of the people to choose me or not," Iranian media quoted him as saying as he registered.
Mr Rafsanjani has said in the past that in his view Ayatollah Khamenei no longer trusts him.
He has also said he does not want a set-up where the two top figures in the Islamic republic are at odds with each other.
But BBC Persian's Kasra Naji says he feels the country is going through a serious crisis and that he can help steer Iran to calmer waters.
Mr Rafsanjani, who was president from 1989 to 1997, leads the Expediency Council, a political arbitration body.