The Pentagon said Friday that the body of a U.S. service member has been recovered in Niger following a militant ambush near the Mali border Wednesday, raising the American death toll to four.

It was not immediately clear how the service member became separated from the unit, precisely when the body was recovered, or if the service member had fallen into enemy hands.

U.S. and Niger troops were conducting a reconnaissance patrol when they encountered dozens of heavily armed militants riding in pickup trucks. A pair of French Mirage fighter jets and other aircraft were scrambled following the attack, presumably to hunt for the missing U.S. service member and provide support for ground units.

On Friday, U.S. officials identified three fallen soldiers as Staff Sgt. Bryan Black, 35, of Puyallup, Washington.; Staff Sgt. Jeremiah Johnson, 39, of Springboro, Ohio; and Staff Sgt. Dustin Wright, 29 of Lyons, Georgia. All were assigned to the Army's 3rd Special Forces Group, which is based at Fort Bragg in North Carolina.

It was unclear Friday if the recovered service member was also a member of 3rd Special Forces Group, the primary unconventional warfare unit operating in Africa.

The Pentagon and the White House have long sought to frame the U.S. military's activities in Niger, and elsewhere on the African continent, as providing support for American allies battling extremists throughout the region – and being removed from direct combat with those groups.

Officials have said the attack occurred during an "advise and assist" mission, a broad term that critics say undercuts the danger associated with training partner nations using only small numbers of troops near militant strongholds.

U.S. forces have expanded efforts in Niger, military officials have said, as part of a growing presence in the Sahel region. The vast expanse of desert stretches across the continent, and affiliates of al-Qaida and the Islamic State have taken advantage of instability in Libya, where arms and fighters flow into a region difficult to govern.

About 800 U.S. personnel are assigned to posts in Niger, mostly at two sites focused on gathering aerial reconnaissance for Nigerian forces. That is an increase from 645 in June. About 300 to the south in Cameroon provide logistical and intelligence support. An unknown but likely small number operate in Mali.

The four combat deaths mark the first known hostile-fire casualties among U.S. forces in Niger. A soldier with the 3rd Special Forces Group was killed in a vehicle accident there in February.