Flag of Mauritania, adopted in 2017. The National Assembly added red stripes to the top and bottom edges to represent “the blood shed by the martyrs of independence”.
Own work, based on this governmental website: http://www.kennach.gov.mr/drapeau.

See  also:
Flags of the World - Mauritania, construction sheet
http://www.kennach.gov.mr/docs/plan01.pdf
http://www.kennach.gov.mr/documents
See File history below for details.