A U.S. Army carry team transfers the remains of Army Staff Sgt. Dustin Wright on Oct. 5 upon arrival at Dover Air Force Base in Delaware. Wright, 29, was one of four U.S. soldiers killed in an ambush by dozens of militants in October. (Staff Sgt. Aaron J. Jenne/U.S. Air Force/AP)

The Pentagon has added Niger, Mali and parts of northern Cameroon to the list of areas where U.S. troops receive imminent danger pay while deployed, a move that reflects the evolving dangers in West Africa and follows the deaths of four U.S. soldiers in Niger last year.

The decision was outlined in a memo signed Monday by Robert Wilkie, the undersecretary of defense for personnel and readiness. The decision was backdated to June 7, meaning the families of the service members killed in Niger and their fellow soldiers will receive back pay for their deployment.

The pay — $225 per month deployed, or $7.50 per day for partial months — was approved as Defense Secretary Jim Mattis reviews final drafts of an investigation of the Oct. 4 ambush in Niger. The final report is expected to be released this month, detailing what went wrong and recommendations for change.

Killed in the battle were Staff Sgt. Jeremiah Johnson, 39; Staff Sgt. Bryan C. Black, 35; Staff Sgt. Dustin Wright, 29; and Sgt. La David Johnson, 25. Black and Wright were elite Green Beret soldiers with the elite 3rd Special Forces Group, while the other two were conventional soldiers deployed with their unit.

The issue of danger pay has been scrutinized in the aftermath of the ambush, in which a force of about 50 armed militants attacked a unit of 11 American and about 30 Nigerien soldiers. U.S. troops deployed in Algeria, Burundi, Chad, Congo, Djibouti, Egypt, Eritrea, Ethiopia, Kenya, Libya, Somalia, Sudan, South Sudan, Tunisia and Uganda already qualified, according to Pentagon pay guidelines.

Troops in Niger, Mali and northern Cameroon previously qualified for $150 in “hazardous duty location pay.” That incentive for U.S. troops was reduced to $100 with the approval of imminent danger pay to meet a Pentagon cap on the incentives when combined.

The issue came up at a House Armed Services Committee hearing on Tuesday, with Rep. Joe Courtney (D-Conn.) asking why Niger and other countries in the area did not qualify while other nations like Algeria and Egypt did. Marine Gen. Thomas D. Waldhauser, the chief of U.S. Africa Command, said a packet submitted to the Pentagon several months ago was still awaiting approval.

Waldhauser was not aware at the time that imminent danger pay for Niger already had been approved, the New York Times first reported Wednesday. A Pentagon spokeswoman, Air Force Maj. Sheryl Klinkel, said the approval was backdated to June 7, before the Niger ambush, because that is when Africa Command initially requested it.

The countries were added to the list as West Africa grapples with militants who have re-branded themselves as Islamic State-West Africa. Al-Qaeda in the Islamic Maghreb (AQIM) also has had a presence in nations including Mali, Niger, Nigeria and Mauritania. Waldhauser said that AQIM groups have consolidated into a group with a new name, Jama’a Nusrat ul-Islam wa al-Muslimin (JNIM), and move freely around northern Mali.