Nabhan had been fighting with the opposition al-Shabab group against the Somali government when he was killed. The Somalia-based group vowed to avenge Nabhan's death and said it would keep on fighting.
"God foiled the endeavor of our stupid enemy who imagined that the flame of jihad in the Muslim lands ... will be extinguished with the killing of the mujahidin leaders," read a statement from the group posted on the internet.
Another unnamed US official said the attack was launched by forces from multiple US military branches and included Navy Seals, at least two army assault helicopters and the involvement of two US warships in the region for months.
The US has not provided official details on the raid or on the number of people killed or where the bodies were taken.