Nabhan, whose nationality is not disclosed, worked for the Belgian Enabel agency, assisting small businesses
The military's Africa Command (Africom) said the strike was carried out on Dec 4.
"The US airstrike was conducted against militants after US and partner forces came under attack," Africom said in a statement late on Wednesday.
"We currently assess this airstrike killed four (4) militants with no civilians involved."
The United States carries out periodic air strikes in Somalia in support of a UN-backed government there, which has been fighting against an al Shabaab insurgency for years.