Morteza Agha-Tehrani, who is aligned with the Iranian president, said Friday Khamenei has told Ahmadinejad he must either accept his candidate for a Cabinet post or resign, The Guardian reported.
Ahmadinejad declined to officially support the ayatollah's reinstatement of Intelligence Minister Hevar Moslehi, who the president had asked to resign.
Agha-Tehrani quoted Ahmadinejad as saying Khamenei "gave me a deadline to make up my mind. I would either accept [the reinstatement] or resign," the British newspaper said.
Ahmadinejad's recalcitrance goes against the traditional fealty Iran's government leaders have shown to the country's supreme leader.
Clerics close to Khamenei have said disobeying Khamenei amounts to apostasy, as he is "God's representative on Earth."
The Guardian said Ahmadinejad reportedly was absent from religious ceremonies this week at Khamenei's house.