"The African Union ... condemns the coup d'Etat and demands the restoration of constitutional legality," said a statement issued at AU headquarters in the Ethiopian capital Addis Ababa.

The statement said AU Peace and Security Commissioner Ramtane Lamamra would travel to Nouakchott immediately "to assess the situation on the ground and to assist in promoting a peaceful solution to the crisis".

It said the AU Peace and Security Council would also hold a meeting soon to consider the situation.

Presidential guards seized Mauritanian President Sidi Mohamed Ould Cheikh Abdallahi on Wednesday after he sacked several top army officers in the country, one of Africa's newest oil producers which also mines iron, copper and gold.

A presidency official who declined to be named said the president, prime minister and interior minister had been arrested and taken to an unknown destination.

Abdallahi won elections last year and took over from a military junta that had ruled since it toppled President Maaouya Ould Sid'Ahmed Taya in a bloodless coup in 2005.