Abdelaziz’s main rivals called the election a charade with “prefabricated results” in a Sunday press conference.
Abdelaziz quit the army after ousting the country’s first elected head of state, Sidi Ould Cheikh Abdallahi, in a coup last August and later stepped down as the head of the junta government to compete as a civilian in the presidential race.
“Firstly we firmly reject these prefabricated results, secondly we call on the international community to put in place an inquiry to shed some light on the electoral process,” the opposition said in a statement.
An opposition spokesman accused Abdelaziz supporters of using fake identity cards to cast multiple votes.
The vote count of more than one-third of the ballots cast Saturday gave a near 52% lead to Abdelaziz – which could mean a victory without the need for a runoff.
Analysts had predicted his win, as the coup leader is deemed highly popular in the impoverished country, which has a history of dictatorship and military coups.
The anti-coup front candidate and parliamentary speaker Messaoud Ould Boulkheir and main opposition leader Ahmed Ould Daddah came in second and third with 16.63% and 13.89% of the votes respectively.
Mauritania has been fighting for democracy and the election was intended to restore constitutional rule and regain international respect.
The African Union suspended Mauritania’s membership while many international donors suspended much-needed aid to the country.