WASHINGTON — The Pentagon has approved danger pay for U.S. troops serving in Niger, Mali and portions of Cameroon, nearly nine months after it was requested by the commander and five months after four American soldiers were killed in an ambush in Niger.

The memo signed Monday by Robert Wilkie, the undersecretary of defense, approves retroactive payments going back to last June 7. That is when the additional money was requested by Gen. Thomas Waldhauser, head of U.S. Africa Command.

Maj. Carla M. Gleason says such requests are evaluated independently, taking into account the combatant commander’s recommendation, the classified risk analysis and any other relevant information. She says it often takes time for the requests to be reviewed and either approved or rejected, but the retroactive pay is typically provided.