Iran's President Hassan Rouhani and leading hardliner Ebrahim Raisi have both been approved to run in elections next month, state media has reported.
However former President Mahmoud Ahmadinejad was barred from standing by a government-controlled vetting body, as was his close ally Hamid Baghaie.
A final list of candidates for the 19 May poll will be announced on 27 April.
More than 1,600 candidates sought to stand, but only about six are selected by the Guardian Council.
The nominations of Mr Rouhani and Mr Raisi will lead to a showdown between bitterly divided political camps.
Mr Rouhani was elected by a landslide in 2013, on a platform of ending the country's diplomatic isolation and creating a freer society.
Two years later his government and six other countries reached a landmark deal, in which Iran agreed to curb its sensitive nuclear activities in return for the lifting of economic sanctions.
Mr Raisi is a seyed, meaning he traces his genealogy back to the Prophet Muhammad. He has a reputation for his uncompromising stance on key issues and is rumoured to be supported by Supreme Leader Ayatollah Ali Khamenei.
Last year the Supreme Leader warned Mr Ahmadinejad that such a move was "not in his interest and that of the country".
Mr Rouhani and Mr Raisi are expected to focus their campaigns on the state of the economy as well as the nuclear deal, which has been hailed by the president as his most significant success over the four years he has been in office.
Other candidates given the go-ahead to compete in the vote are Mostafa Mirsalim, Tehran mayor Mohammad Bagher Ghalibaf, Mostafa Hashemitaba and Vice President Eshaq Jahangiri.