NOUAKCHOTT (Reuters) - Mauritanian President Mohamed Ould Abdel Aziz has won another five-year term with 82 percent of the vote, officials said on Sunday, after an election boycotted by most of the opposition.

Abdel Aziz, an ally of Western powers in the fight against al Qaeda-linked Islamists in West Africa, faced no major challenger to his rule in Saturday's election in his vast desert nation, which straddles black and Arab Africa.

Opposition parties also boycotted last year's parliamentary elections, saying the organisers were biased and the process flawed. Talks to persuade them to take part in Saturday's presidential election broke down in April.

Abdel Aziz's closest rival, anti-slavery campaigner Biram Ould Dah Ould Abeid, came in distant second place with nine percent of the vote, the head of the national election commissionAbdellahi Ould Soueid Ahmed, told a news conference.

Turnout was 56 percent, said Soueid Ahmed.

Abdel Aziz came to power in an army coup in 2008 and won a contested election the following year.