Iran's hardline former president Mahmoud Ahmadinejad on Wednesday registered to run again in an election in June that's being seen as a test of the legitimacy of the country's clerical rulers. Vilified in the West for his questioning of the Holocaust, Ahmadinejad had to step down in 2013 because of term-limit rules, when incumbent President Hassan Rouhani, who negotiated Iran's 2015 nuclear deal with world powers, won in a landslide. "People should be involved in Iran's decision-making process," state TV quoted Mr Ahmadinejad as saying after registering. "We must all prepare ourselves for fundamental reform." Candidates began signing up for the polls on Tuesday with the clerical rulers hoping for a high turnout that may be hit by rising discontent over an economy crippled by US sanctions reimposed after Washington exited the nuclear deal three years ago. Registration will end on Saturday, after which entrants will be screened for their political and Islamic qualifications by a 12-member vetting body, the Guardian Council. Six members of the hardline body are appointed by Supreme Leader Ayatollah Ali Khamenei. Mr Khamenei backed Ahmadinejad after his 2009 re-election triggered protests in which dozens of people were killed and hundreds arrested, rattling the ruling theocracy, before security forces led by the elite Islamic Revolutionary Guard Corps (IRGC) stamped out the unrest. But a rift developed between the two after then-president Ahmadinejad explicitly advocated checks on Mr Khamenei's ultimate authority. Mr Ahmadinejad was disqualified by the Guardian Council in the 2017 presidential election.