Mauritanians are voting for the first time since the country gained independence from France in 1960.
The 62-year-old is standing down after serving the maximum two five-year elected terms.
However the status quo is likely to prevail when a new leader is elected.
Abdel Aziz has expressed his support for Mohamed Ould Ghazouani, who is a former general and defense minister.
Netanyahu orders deeper Israeli incursion into Lebanon
Israeli Prime Minister Benjamin Netanyahu said on Sunday he had ordered troops to move further into Lebanon in the battle against Hezbollah, despite a ceasefire announced more than six weeks ago.
US military says it turned away blockade runner trying to reach Iranian port
The US military has announced that it fired a missile into the engine room of a vessel trying to get through the US blockade of Iran on Friday.
Two hundred hurt in post-game violence as Paris hails second Champions League triumph
More than 200 people were injured and one person died in Paris following Paris Saint-Germain's second consecutive Champions League win, the interior ministry said on Sunday, reviving France's heated debate about street violence.
Illegal mine collapses in China, killing five just days after Shanxi disaster
A mine shaft collapse during an illegal mining operation in China's southwestern Yunnan province killed five people and injured one, state media reported, days after the country's deadliest mining accident since 2009 left at least 82 dead.
Israel troops capture Beaufort Castle in southern Lebanon push against Hezbollah
Israeli troops have seized the 900-year-old Beaufort Castle and its strategic ridge in southern Lebanon, the military said on Sunday, a major advance against Hezbollah despite a ceasefire announced more than six weeks ago.
