The first change will see part of one infantry unit, around 800 troops, replaced with a similar number of military trainers and advisors to support local forces in "spotlight African countries," Defense Department officials said.

"The message I'm relaying to my (African) partners is we are not walking away," US Army Africa commander Major General Roger Cloutier told reporters.

"We are still engaged."

The move is the first resulting from a sweeping Pentagon review of the presence of US forces around the world in an effort to better align that presence with US defense priorities -- which list China and Russia as the principle threats to the country.

That could mean reducing US deployments meant to confront Islamic militant threats, including in Africa.

But the Pentagon is also wary of leaving a vacuum in certain areas, like in Africa, for the Chinese and Russians to fill, which could give them strategically valuable footholds.

The United States has about 6,000 military personnel throughout Africa, including 800 in West Africa, 500 Special Forces in Somalia and an unspecified number at an air base in Niger.

The US depends especially on French and various African partner forces in West Africa in field operations, but the US strategy has moved to mostly seeking to "contain" the extremist groups rather than degrade them.

"The terrorist threat in Africa remains persistent and, in many places, is growing," said the Pentagon's inspector general in a recent report on US counterterrorism operations in Africa.