Navy Captain Jeff Davis, a Pentagon spokesman, says Somali forces who were going after a bomb-making network in the Puntland region came under small arms fire from enemy fighters.
Davis says there were US military advisers with the Somali forces, and the US launched a defensive airstrike to protect them.
He says the military is looking into reports that the people killed in the strike may not have been enemy fighters. He says no US forces were injured.
This is the second airstrike this week that the US carried out against al-Qaida-linked al-Shabab militants in Somalia.