The Takfiri al-Shabab terrorist group has claimed responsibility for the attack, which took place on Monday in Jana Cabdalle village in the country’s southern region of Jubbaland.
Mohamed Ahmed Sabriye, director of communications of Jubbaland state palace who confirmed the deaths, said the car bomb exploded outside the base of Somali special forces trained by the US called Danab.
"Two soldiers of Danab (special) forces died and two others were wounded. A US officer was seriously wounded," Sabriye told Reuters.
He later said one of the wounded soldiers in the attack had subsequently died.
However, al-Shabab claimed that more people have been killed in the attack.
"We attacked US and Somali forces called Danab in Jana Cabdalle village with a suicide car bomb. We killed four US officers, and 16 Somali forces which they trained," the military operations spokesman of the al-Shabab group, Abdiasis Abu Musab, said in a statement.
"We also wounded 12 Somali soldiers. We also destroyed 3 US armored vehicles.”
Jana Cabdalle village is located some 60 km (around 40 miles) from the port city of Kismayu, which is the commercial capital of Jubbaland. The southern Somali region is still partly controled by al-Shabab.