The appointment comes hours after Ismail Ould Cheikh Sidiya and his entire government resigned without giving any reason amid an investigation into alleged high-level corruption.
Although the ruling party candidate won the first democratic transition to power since 1960, he's also a close confidante of his predecessor who came to power after instigating a coup in 2008.
Mauritania's electoral commission has proclaimed ruling party candidate Mohamed Ould Ghazouani winner with 52 percent of votes in a presidential election the previous day.
As Ould Abdel Aziz steps down after two terms, will his close ally Ould Cheikh Mohamed Ahmed Ghazouani take over in a country that has been wracked by coups since 1978?
A record 98 parties will take part in legislative, regional and local elections for which more than 1.4 million people are registered. Potential run-off elections would take place on September 15.
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