Mauritanians will go to the polls on June 22 to vote for a successor to President Mohamed Ould Abdel Aziz, who is stepping down after his second and final term in office.
If there is no outright winner in the first round of elections, a runoff vote will be held on July 6, under a presidential decree seen by AFP.
Candidates have until May 8 to file their bid to be next president of the conservative West African desert state.
Abdel Aziz, a 62-year-old former general, was a major figure in a successful coup in 2005, and in 2008 led another coup that forced out the then president, Sidi Ould Cheikh Abadallahi.
Elections were staged in 2009, which Abdel Aziz won. He was returned to office in elections in 2014, winning in the first round.
Several major figures have already declared their intentions to run.
They include former defence minister Mohamed Ould Cheikh Mohamed Ahmed, who is a close associate of the current president.
Others are the former head of the 2005-2007 transitional government, Sidi Mohamed Ould Boubacar; anti-slavery activist Biram Ould Dah Ould Abeid; and long-standing opposition figure Mohamed Ould Moloud.