Iran's former nuclear negotiator Hassan Rowhani joined the race to succeed President Mahmoud Ahmadinejad on Thursday, accusing the incumbent of needlessly incurring crippling economic sanctions.

Rowhani, 64, who headed the relatively moderate nuclear negotiating team that served under reformist president Mohammad Khatami before Ahmadinejad took power in 2005, joins a field of more than a dozen hopefuls for the June election.

Ahmadinejad, who fired Rowhani on taking office, is barred by the constitution from standing for a third consecutive four-year term.

In 2003 Rowhani led the talks with the West at which Tehran agreed on a moratorium on its nuclear drive. The suspension lasted for around two years.

In a speech to supporters in Tehran, Rowhani pledged that if elected he would rescue the sharply deteriorating economy by mending relations with the international community.

"I have come forward to save Iran's economy and forge a constructive interaction with the world through a government of wisdom and hope," Iranian media quoted him as saying.

"This administration made fun of sanctions, deriding them as scrap paper, while we could have avoided them or to some extent reduced" their effect.

Rowhani was referring to a speech by Ahmadinejad in which he famously dismissed the six separate resolutions adopted by the UN Security Council over Iran's nuclear programme as "scrap paper."

Rowhani took aim at the sharp depreciation of the rial over the past year in the face of EU and US sanctions targeting Iran's oil exports and banking system.

"The value of our currency has been halved and they (the current administration) are still shouting slogans," the moderate conservative said.

All presidential hopefuls have to be vetted by the Guardians Council, an unelected body controlled by religious conservatives appointed by supreme leader Ayatollah Ali Khamenei.

The council has until May 22 to announce the final list of candidates.

Other hopefuls include Ali Akbar Velayati who was foreign minister from 1981 to 1997 and is the current foreign affairs adviser to Khamenei, and Mohammad Baqer Qalibaf, a former national police chief who is currently mayor of Tehran.

Neither Khatami nor his moderate conservative predecessor Akbar Hashemi Rafsanjani will stand for a new term, according to their close relatives.

But Khatami's first vice president, Mohammad Reza Aref, has announced his willingness to be a candidate.

The June 14 election will be followed closely in the West four years after Ahmadinejad's re-election sparked violent protests that the regime suppressed with deadly force.