Jihadists from Somalia's Al-Shabaab group on Sunday stormed a military base used by US forces in Kenya's coastal Lamu region, destroying aircraft and military vehicles, according to Kenyan police and army officials.
A group of attackers breached security at Camp Simba in the early hours but were repelled and four jihadists were killed, said army Colonel Paul Njuguna.
Al-Shabaab has launched regular cross-border attacks since Kenya sent troops into Somalia in 2011 as part of an African Union force protecting the internationally backed government -- which the jihadists have been trying to overthrow for more than a decade.
Lamu region, which includes the Lamu Island tourist hub, lies close to the Somali frontier and has suffered frequent attacks often carried out with roadside bombs.
Njuguna said "an attempt was made to breach security at Manda Air Strip" at 5:30am but the attack was repulsed.
"Four terrorists' bodies have so far been found. The airstrip is safe," he said, adding that a fire had broken out but had since been dealt with.
An internal police report seen by AFP said two aircraft, two American helicopters and "multiple American vehicles" were destroyed at the airstrip.
Local police commissioner Irungu Macharia said five people had been arrested near the camp and were being interrogated.
It was not yet known if there were casualties among Kenyan or American troops.
US military officials confirmed the attack and said US and Kenyan forces had repelled the Al-Shabaab fighters.
"Working alongside our Kenyan partners, the airfield is cleared and still in the process of being fully secured," said the US Africa Command (AFRICOM) in a statement.
The nearby civilian airport at Manda Bay, which brings tourists visiting Lamu Island -- a UNESCO World Heritage Site -- was closed for several hours after the incident, according to the civil aviation authority.
Al-Shabaab said in a statement it had "successfully stormed the heavily fortified military base and have now taken effective control of part of the base".
AFRICOM accused Al-Shabaab of lying in order to create false headlines.
US military network
The Somali jihadists have staged several large-scale attacks inside Kenya in retaliation for Nairobi sending troops into Somalia as well as to target foreign interests.
The group has been fighting to overthrow an internationally-backed government in Mogadishu since 2006, staging regular attacks on government buildings, hotels, security checkpoints and military bases in the country
Despite years of costly efforts to fight Al-Shabaab, the group on December 28 managed to detonate a vehicle packed with explosives in Mogadishu, killing 81 people.
The spate of attacks highlights the group's resilience and capacity to inflict mass casualties at home and in the region, despite losing control of major urban areas in Somalia.
In a November report, a UN panel of experts on Somalia noted an "unprecedented number" of homemade bombs and other attacks across the Kenya-Somalia border in June and July last year.
On Thursday, at least three people were killed when suspected Al-Shabaab gunmen ambushed a bus travelling in the area.
According to the Institute for Security Studies, the United States has 34 known military bases in Africa, from where it conducts "drone operations, training, military exercises, direct action and humanitarian activities".
US military strikes in Somalia surged after President Donald Trump declared the south of the country an "area of active hostilities".
AFRICOM said in April it had killed more than 800 people in 110 strikes in Somalia since April 2017.