Mr Masra, a former opposition leader, signed a reconciliation deal with Mr Déby after his return from exile, before he was appointed prime minister in January.

He told supporters at a rally on Sunday that he was seeking the top seat so as to unite the people and "heal hearts".

The opposition have criticised the move, saying it’s a ploy to give the appearance of pluralism to an election which Mr Déby is certain to win.

It is "a farce, a fake candidacy to accompany the head of military power", Max Kemkoye, the spokesman of a group of opposition parties GCAP, told the AFP news agency.

Mr Déby's main rival, opposition leader Yaya Dillo, was killed in a shootout with security forces on 28 February. The government had blamed him for a deadly attack on the country's security agency, which he denied.

He was widely predicted to be the main opponent of Mr Déby in the election.

Mr Déby took over as Chad’s leader after his father was killed by rebels after three decades in power.