One US service member and two Department of Defence contractors were killed by an al Qaida-linked group during an attack on a military base in Kenya.
Al Shabab extremists overran the base in Manda Bay used by US counter-terror forces before dawn on Sunday, destroying American aircraft and vehicles, Kenyan authorities have said.
It was the group's first attack against US forces in the east African country.
US Africa Command confirmed three were killed in the attack while two other Department of Defence members were wounded.
They are in a stable condition and being evacuated. Kenyan military spokesman Paul Njuguna said five attackers were dead.
Al-Shabab, based in neighbouring Somalia, claimed responsibility.
In a statement, US Africa Command said: “The attack on the compound today involved indirect and small arms fire.
“After an initial penetration of the perimeter, Kenya Defense Forces and US Africa Command repelled the al-Shabaab attack.
“Reports indicate that six contractor-operated civilian aircraft were damaged to some degree.
“Manda Bay Airfield is utilised by US forces whose missions include providing training to our African partners, responding to crises, and protecting US interests in this strategically important area.”
Kenya is a key base for fighting al Shabab, one of the world's most resilient extremist organisations.
A large plume of black smoke rose above the airfield Sunday and residents said a car bomb had exploded.
Lamu county commissioner Irungu Macharia said five suspects were arrested and were being interrogated.
An internal Kenyan police report seen by the Associated Press said two fixed-wing aircraft - a US Cessna and a Kenyan one - were destroyed along with two US helicopters and multiple US vehicles at the Manda Bay military airstrip.
The report said explosions were heard at around 5.30am from the direction of the airstrip.
The scene, now secured, indicated that al Shabab likely entered "to conduct targeted attacks", the report said.
The Kenya Civil Aviation Authority said the airstrip was closed for all operations.