Mohammad Reza Aref, a pro-reform candidate in Iran's upcoming presidential election, said he was pulling out Tuesday.
His withdrawal follows calls for reformists to avoid splitting the vote and rally around moderate candidate Hassan Rowhani.
Aref announced his decision to withdraw on his campaign website, CNN reported.
He was the second candidate to withdraw within a few hours, following Gholam-Ali Haddad Adel, who dropped out without offering a reason.
Aref, however, said former reformist president Mohammad Khatami, with whom he is known to be close, had sent him a letter advising that his candidacy was "not in the interest" of Iran's reformers, the Associated Press reported.
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Khatami served as Iran's president from 1997 to 2005 and Aref, 62, was his vice president from 2001 to 2005.
Aref said on his website, "On Monday evening, I received a letter from Mr. Mohammad Khatami and decided my presence to the election is not beneficial to overall reform."
He also served as a top security official under the moderate former president, Akbar Hashemi Rafsanjani, and still reportedly enjoys his support.
Aref was quoted as saying at a rally Monday in the western Iranian province of Kurdistan, "I will follow the paths of Khatami and Rafsanjani. I do not approve of the current foreign policy. We should try to have good [international] interactions to gradually reduce the sanctions and finally remove them."
While Aref himself is not a cleric, he is a member of the Expediency Council, which mediates between Iran's parliament and the non-elected Guardian Council, made up of Imams.
Meanwhile, conservatives have also been working to avoid splitting the vote.
Under the Iranian system, if no candidate gets a majority the vote goes to a run-off between the top two candidates.
The June 14 election will choose a successor for outgoing President Mahmoud Ahmadinejad who cannot run for another term under Iran's law.
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