Reuters. Former foreign minister Mottaki joins Iran's presidential race

Former Iranian Foreign Minister Manouchehr Mottaki has announced he will run for president in an election in June likely to be dominated by seething conservative rivalries.

The presidential poll is a crucial test for Iran after the last one in 2009 ignited mass street protests in Tehran and other cities after Mahmoud Ahmadinejad's disputed re-election.

As Iran remains locked in a stand-off with world powers over its nuclear program, rifts between Ahmadinejad and rivals loyal to Supreme Leader Ayatollah Ali Khamenei threaten to tarnish the legitimacy of the state's theocratic ruling system.

To prevent the next president from challenging Khamenei's authority, his close advisers are looking to unite around a single hard-line candidate to minimize chances of the virulent political divisions leading to post-election chaos.

The Supreme Leader controls the Council of Guardians, which oversees elections and can bar candidates from standing.

Reformists are unlikely to be allowed to run unless they distance themselves from Mir Hossein Mousavi and Mehdi Karoubi, who lost out in the 2009 election and who have been under house arrest for more than two years for "seditious acts".

Both opposition leaders said the 2009 vote was rigged and their supporters took to the streets in huge numbers to protest, only to be crushed by security forces and religious militia.