Somalia’s al-Shabaab terror group targeted US forces in neighbouring Kenya for the first time on Sunday, killing three people and destroying American reconnaissance aircraft during an attack on a secretive military base.

An unknown number of jihadist militants struck at Camp Simba, an American military facility located on a Kenyan naval base, shortly before dawn. The US military said one US service member and two contractors had been killed, while two while two Department of Defence officials were wounded.

There were “fewer than 150” American soldiers at Camp Simba, which is located on Manda Bay close to the tourist resort of Lamu, when the attack took place, US officials said.

Although the militants were unable to penetrate Camp Simba itself, they succeeded in overrunning an adjacent airfield where they set ablaze at least two planes, one of which was an American “Intelligence, Surveillance and Reconnaissance” aircraft used for missions in Somalia.

The brazen nature of the attack — which took place more than 50 miles south of the Somali frontier — represents a significant escalation in al-Shabaab cross-border operations.

The group has frequently carried out attacks on Kenyan troops in retaliation for the Kenyan army’s military incursion into southern Somalia.

But until now it has shied away from attacking US troops stationed in Kenya, although the group did mount mount a failed operation against American forces stationed in Somalia last September.