In a letter to Congress, Obama says the forces will focus on "intelligence sharing" with French troops fighting Islamist militants in neighboring Mali. He says the American forces have been deployed with weapons, quote, "for the purpose of providing their own force protection and security."

The U.S. and Niger signed agreement last month spelling out legal protections and obligations of Americans who might operate from the African nation. But U.S. officials declined at the time to discuss specific plans for a military presence in Niger.

The Pentagon is also considering plans to base unarmed spy drones in Niger to boost its ability to see what is happening in the region.