From the U.S. State Department:

The U.S. Department of State warns U.S. citizens of the risks of traveling to Mauritania, and urges extreme caution for those who choose to travel to Mauritania, because of activities by terrorist groups in the region, including al-Qaida in the Islamic Maghreb (AQIM). AQIM continues to demonstrate its intent and ability to conduct attacks against foreign nationals, including U.S. citizens. ...

The U.S. Embassy in Nouakchott recommends against all non-essential travel to the border regions of Guidimagha, the Hodh El Charghi and Hodh El Gharbi regions of southeastern Mauritania, the eastern half of the Assaba region (east of Kiffa), the eastern half of the Tagant region (east of Tidjika), the eastern half of the Adrar region (east of Chinguetti), and the Zemmour region of northern Mauritania because of the security risk and the threat of kidnapping to Westerners by terrorist groups. ...

U.S. State Department Warning