Tehran's ex-prosecutor and controversial ally of President Mahmoud Ahmadinejad has been released from Evin prison after spending almost two days in detention, Iranian media reported.

The reports on Wednesday did not elaborate on the circumstances of Saeed Mortazavi's release nor of his arrest on Monday night when he was sent to Evin, where many political prisoners and journalists have been imprisoned over years on his orders.

Mortazavi's detention, amid a brewing political fight between state branches, was criticised by Ahmadinejad as a "very ugly action".

Despite strong opposition from the parliament, Mortazavi is caretaker of Iran's wealthy social welfare organisation.