Iran's former president Mohammad Khatami is to withdraw his candidacy from the country's June presidential election, the BBC understands.
Mr Khatami was president of Iran from 1997-2005 and was succeeded by Mahmoud Ahmadinejad, a conservative.
Mr Ahmadinejad is expected to stand for re-election.
An unnamed ally did not give a reason for the withdrawal, and neither did he name the candidate whom Mr Khatami would be supporting.
Mr Khatami was the most liberal president since the revolution.
But he entered this campaign reluctantly and unenthusiastically, says the BBC's Jon Leyne in Tehran, and it soon became clear that many of those in power in Iran did not want him to return as president. One city prevented Mr Khatami from campaigning with the excuse that it would cause traffic jams.
His withdrawal therefore comes as no surprise, says our correspondent, and Mr Khatami is now expected to endorse former Prime Minister Mir Hossein Mousavi.
The decision also leaves Mr Ahmadinejad in a stronger position, our correspondent adds.