Photo: Xinhua

Jihadists from Somalia's Al-Shabaab group on Sunday stormed a military base used by US forces in Kenya's coastal Lamu region, killing three US citizens and destroying several aircraft and military vehicles, officials said.

Attackers breached heavy security at Camp Simba at dawn but were pushed back and four jihadists killed, said army spokesman Colonel Paul Njuguna. 

The US military, however, said three US citizens died in the attack including a service member and two civilian defense contractors.

"Our thoughts and prayers are with the families and friends of our teammates who lost their lives today," General Stephen Townsend, the head of US Africa Command, said in a statement.

Two other US Department of Defense personnel were wounded, the statement added, without giving further details.

Al-Shabaab has launched regular cross-border raids 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.

The Lamu region, which includes popular tourist beach destination Lamu Island, 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 5:30 am but it 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.

Kenya's Inspector General of Police Hilary Mutyambai said officers were "on high alert" after the attack.

An internal police report seen by AFP said two Cessna aircraft, two US helicopters and "multiple American vehicles" were destroyed at the airstrip. 

According to the Institute for Security Studies, the US has 34 known military bases in Africa, from where it conducts "drone operations, training, military exercises, direct action and humanitarian activities."