A US commando has been killed and four others wounded when they came under fire in Somalia during an operation against al-Shabaab militants, the US military says.

The US special operations forces were fighting on Friday alongside about 800 troops from the Somali National Security Forces and Kenyan Defence Forces when they were attacked by mortars and small arms fire.

One local soldier was also wounded in the attack, the US military said in a statement, without clarifying whether that fighter was part of the Somali or Kenyan armed forces.

Although one of the wounded Americans did not receive additional care after being treated in the field, the other three and the wounded local soldier were medically evacuated for follow-up care.

– AAP