A military helicopter crash in Kenya near the border with Somalia has killed at least eight people, officials said Tuesday.

It was not immediately clear what caused the crash in the county of Lamu in coastal Kenya. Kenyan defense forces operate in the area to help deter the al-Qaida-linked al-Shabab group, based across the border in Somalia.

The Department of Defense (DoD) said the Air Force helicopter crashed while on night patrol.

“A Board of Inquiry has been constituted and dispatched to the scene to establish the cause of the crash,” the statement added.

Security agents speaking on condition of anonymity because they were not authorised to speak to reporters told The Associated Press that all military personnel and crew on board the helicopter died.

But the DoD which said it “condole(s) with the families of the crew” did not mention how many people were killed.

Kenyan troops are also in Somalia under the African Union Transition Mission in Somalia to help in fighting al-Shabab. The Kenyan forces deployed to Somalia in 2011, but there are now plans to withdraw the multinational forces as Somali troops take over responsibility for their country’s security.

Al-Shabab has increased attacks in Kenya in recent months, killing dozens of people in the border region as the rebels feel pressure from a Somali military offensive launched last year after the election of Hassan Sheikh Mohamud as president in May.