Iran's former moderate president Akbar Hashemi Rafsanjani has endorsed ally Hassan Rouhani in the June 14 election, saying the candidate is "more suitable" than others for the presidency.

Rouhani was Iran's former top nuclear negotiator under former president Mohammad Khatami and served as top security official under Rafsanjani.

"I will vote for Dr Rouhani, who entered the race after consulting me," Rafsanjani said in remarks reported by ILNA news agency on Tuesday.

"I consider him to be more suitable (than other candidates) to steer the executive branch," he said referring to the slate of five other hopefuls, most of whom are conservatives.

Earlier on Tuesday, Mohammad-Reza Aref, the sole reformist candidate in the presidential vote, withdrew from the race after receiving advice from Khatami, his website has reported.

"At dusk on Monday... I received a letter from Mohammad Khatami... he said it would not be wise for me to remain in the race," Aref wrote in his withdrawal statement on Tuesday.

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In recent days, calls have grown from within the reformist camp for Aref to quit in favour of Rouhani.

Aref 's withdrawal from the race is the second in two days.

Ex-parliamentary speaker Gholam-Ali Haddad Adel, seen as close to Supreme Leader Ayatollah Ali Khamenei, pulled out of the race on Monday without endorsing any of the four remaining conservatives standing for election.

He was not considered a frontrunner in the presidential poll.

Khatami's advisory council in a statement threw their backing behind Rouhani as the "reformist camp candidate".

Source: Agencies