Tehran- Candidate registration started Tuesday at the Interior Ministry for Iran's presidential election, with President Mahmoud Ahmadinejad facing tough opposition in the June 12 vote.

The registration will continue for five days and at the end of this month the Guardian Council, in charge of checking the ideological qualification of the candidates, will announce the names of those selected to run in the election.

President Ahmadinejad's main challengers are likely to be former prime minister Mir-Hossein Moussavi and National Trust Party chairman Mehdi Karroubi, both considered moderate and critics of Ahmadinejad's policies.

Another candidate is the former commander of the Revolutionary Guards, Mohsen Rezaei, a conservative who is also critical of Ahmadinejad's economic policies.

Observers believe the main competition will be between Ahmadinejad and Moussavi, the latter openly supported by ex-presidents Akbar Hashemi-Rafsanjani and Mohammad Khatami.

The president on Monday cancelled a visit to Latin America in order to have more time for his election campaign. Instead of Brazil, Venezuela and Ecuador, Ahmadinejad will go to Qazvin province later this week. (dpa)