Hamdi Ould Mahjoub said that Aziz was shot in the arm when the military unit opened fire on his convoy. The president was returning from a trip to the desert and the incident occurred 40 kilometers (24 miles) north of the capital.
Mahjoun said the president's life was not in danger. He is being treated at the military hospital in Nouakchott.
It's unclear why the military opened fire on the presidential motorcade Saturday, but reports in local media indicated the military unit had not been told of the president's trip.
Mauritania has been destabilized by an al-Qaida affiliate, which has launched attacks in Mauritania from neighboring Mali.