Former President Mohammad Khatami of Iran is to seek the presidency of Iran again.
Mr Khatami, was in office from 1997 to 2005 and was seen as pushing for detente with the West during that time.
Ties with the West have deteriorated under President Mahmoud Ahmadinejad over the past four years amid tensions over Iran's nuclear programme.
The West accuses Iran of seeking to build nuclear weapons. Tehran insists its aim is domestic electricity.
Three rounds of sanctions have been imposed by the UN Security Council.
Elections are due in June. Iran's top authority is Supreme Leader Ayatollah Ali Khamenei.
President Barack Obama has offered a new US approach to engage Iran, saying he would extend a hand of peace if the Islamic Republic would "unclench its fist".