DAKAR, Senegal (AP) — The head of the U.S. military in Africa says it has taken steps to increase the security of troops on the ground, adding armed drones and armored vehicles and taking a harder look at when American forces go out with local troops.

The U.S. Africa Command chief says in an interview that the U.S. also has cut the response time needed for medical evacuations — the result of a broad review in the wake of last year's ambush in Niger that killed four U.S. soldiers and four of their Niger counterparts.

Gen. Thomas D. Waldhauser says a report is due in mid-August on actions taken in response to the findings.

He says Africa's challenges remain vast, from Islamic State and al-Qaida-linked groups in the west to al-Shabab in the east.