Senior Al-Shabaab leaders said that the drone attacks were carried out early on Thursday in the outskirts of Kismayu town, killing nine women and children and wounding 30 others.
Kismayu, which is located 528 kilometers south of Mogadishu, is the largest Somali port controlled by al-Shabab.
Over the past few weeks, numerous US remote-controlled drones have crashed in Somalia.
Somalia is the sixth country where the US military has used pilotless aircraft to conduct deadly bombing strikes.