A former Iranian nuclear negotiator announced on Thursday he would run for president, the most moderate contender so far to bid to succeed Mahmoud Ahmadinejad in a June election dominated by conservatives.
Hassan Rohani, 64, was head of the powerful Supreme National Security Council under presidents Ali Akbar Rafsanjani, considered a master of realpolitik rather than an ideologue, and Mohammad Khatami, who pushed for wide-ranging social and political reforms.
Rohani, a Muslim cleric, presided over talks with Britain, France and Germany that saw Iran agree to suspend uranium enrichment-related activities between 2003 and 2005.
He resigned after Ahmadinejad took office in August that year. The nuclear work was resumed and Rohani was derided for being too accommodating in negotiations.
During Ahmadinejad's two terms in office, tensions with the West over Iran's nuclear programme have worsened, with the United States and Europe imposing sanctions on its oil and banks over suspicions Tehran is seeking atomic arms, which it denies.
"We need a new management for the country but not based on quarrelling, inconsistency and eroding domestic capacity, but through unity, consensus and attracting honest and efficient people," Rohani told a gathering of supporters on Thursday, Iran's Mehr news agency reported.
The June election is Iran's first presidential poll since 2009 when mass street protests erupted against Ahmadinejad's disputed re-election.
The defeated reformist candidates in that election, Mirhossein Mousavi and Mehdi Karoubi, who became figureheads for the "Green movement" - which mounted Iran's biggest street protests since the Islamic revolution in 1979 - have been under house arrest for more than two years.
It is unclear whether the Guardian Council, a state body that can veto candidates, will allow reformists to run, but barring too many contenders risks destroying public interest in a vote which bolsters Iran's claims to democratic legitimacy.
A former Western ambassador to Iran who had dealings with Rohani during the Khatami administration described him as "approachable and no-nonsense," likely to be "a calm, orthodox, efficient and straightforward servant ... and less a charismatic or an independent figure".
With nuclear policy directed by supreme leader Ayatollah Ali Khamenei rather than the president, the election is not likely to produce any tangible policy shift there.
"My government will be one of prudence and hope and my message is about saving the economy, reviving ethics and interaction with the world," Rohani said in a critique of Ahmadinejad's economic record.
"Inflation is above 30 percent, the reduction in the value of the national currency, unemployment and zero economic growth are among the country's problems."
While Rafsanjani was not present for the announcement, his son and daughter, Yasser and Fatemeh Hashemi, attended the event, an apparent indication of the former president's support for Rohani, his long-serving protege.
Also attending Rohani's announcement was Mahmoud Alavi, a member of Iran's Assembly of Experts, the body responsible for overseeing the actions of supreme leader Khamenei - indicating he has some status inside Iran's establishment.
Hooman Majd, a New York-based Iranian-American journalist and author, said Rohani - head of an Iranian think-tank, the Centre for Strategic Research - might attract some voters looking for change, without being radical enough to risk being banned.
"Rohani has been a loyal soldier of Khamenei and is not considered a threat to the system. I think it would be too much for the Guardian Council to disqualify someone like that," Majd said.
"Rohani's not a personality people know very well but he could be viable with support from the Rafsanjani camp and a modern youthful campaign."
Khamenei's close advisers plan to put forward their own candidate, hoping to minimise the chances of the next president mounting challenges to the leader's authority, as they accuse Ahmadinejad of doing, especially during his second term.
Khamenei loyalists accuse Ahmadinejad of trying to erode the influence of the clergy and the supreme leader and fear he will try to extend his political influence after his final term ends in June by helping a close ally win the election.
The most likely candidate from the Ahmadinejad camp is his former chief of staff, Esfandiar Rahim Mashaei, but there has been no official word so far on whether he will try to run.