A number of Cameroonian troops have gone missing after Boko Haram militants attacked the northern town of Bonderi on the border with Nigeria, a Cameroonian security official said Thursday.

“We are certain that the assailants are Boko Haram militants,” the official told Anadolu Agency. “We are saddened to have lost some of our men.”

The official added that a number of Cameroonian military vehicles had been seized during clashes with the militants, which erupted in the early hours of Thursday.

He went on to say that reports on the incident – and the casualties that accompanied it – had yet to be finalized.

This is the second attack this month on the border town by suspected Boko Haram militants.

On August 6, the town’s police station came under rocket attack. Cameroonian officials said six Boko Haram militants had been killed in subsequent clashes, while several Cameroonian police vehicles had been seized by militants.

Boko Haram turned violent in 2009 following the extrajudicial murder of leader Mohamed Yusuf while in police custody.

The group has since been blamed for the destruction of public infrastructure and private businesses, along with the displacement of at least six million people in northern Nigeria.