The Kenya Police report said two U.S. helicopters and a Cessna aircraft had been destroyed as well as “multiple” American military vehicles. A Kenyan Cessna aircraft was also destroyed, it said.
In a statement earlier on Sunday al Shabaab claimed they had destroyed seven aircraft and three military vehicles, without providing other details. It also published pictures of masked gunmen standing next to an aircraft in flames.
Major Karl Wiest from AFRICOM told Reuters fewer than 150 U.S. personnel were at the base, where they provide training and counter-terrorism support to East African forces.
“Initial reports reflect damage to infrastructure and equipment. An accountability of personnel assessment is underway,” AFRICOM said in a press release.
The assault that began before dawn lasted around four hours, witnesses and military sources told Reuters.
Kenyan military spokesman Colonel Paul Njuguna said the base had been secured.
“This morning at around 5:30 am an attempt was made to breach security at Manda Air Strip. The attempted breach was successfully repulsed,” he said in a statement.
“Arising from the unsuccessful breach a fire broke out affecting some of the fuel tanks located at the airstrip. The fire has been put under control.”
In the operation to repulse the attack, at least five militants were killed and weapons including four AK47 rifles were seized, Njuguna said.
There was no indication that the militants had managed to enter the base. The airfield is separate to another on Manda Island used by commercial flights to Lamu.
Al Shabaab has been fighting for more than a decade to overthrow the Somali government and impose strict Islamic law.
Kenya sent troops into Somalia in 2011 after a spate of cross-border attacks and kidnappings. They were later absorbed into an African Union peacekeeping force, now 21,000-strong, which supports the shaky, Western-backed Somali government.
EXPLOSION IN THE DARK
Independent investigator Benjamin Strick, who analyses satellite imagery for open source investigation websites such as Bellingcat, said the photos of gunmen next to a burning plane published by al Shabaab matched satellite images of buildings and a distinctive aircraft apron adjacent to the base but outside its perimeter.
Residents on nearby Lamu Island, a haven for wealthy tourists and visiting European royalty, say a loud explosion jolted them awake before 4 a.m.
Abdalla Barghash said he later saw a large dark plume of smoke rising from the Manda Bay mainland, where the airstrip and base are located.
Lamu county, which is far more impoverished than the island, is frequently targeted by al Shabaab with roadside bombs and ambushes on travelers or attacks on isolated villages.
The insurgents killed three passengers when they attacked a bus in the county on Thursday. (Reuters)
Additional reporting by Humphrey Malalo, Feisal Omar and Katharine Houreld. Writing by Katharine Houreld and Elias Biryabarema; Editing by Raissa Kasolowsky and Gareth Jones