Cameroonian soldiers killed 20 Boko Haram fighters on Wednesday during a raid in northern Nigeria carried out by a multinational force tasked with stamping out the Islamist militants, military sources told Reuters on Thursday.

Cameroon commander General Jacob Kodji said the Islamist fighters were killed in the Nigerian town of Djibrila, which is about 10 km (six miles) from the Cameroon border.

A spokesman for Cameroon's Defence Ministry, Colonel Didier Badjeck, said 12 hostages were freed and munitions and armoured vehicles were seized during the operation.

Boko Haram wants to establish an Islamist state in northeastern Nigeria and has waged a six-year campaign of violence to that end, killing thousands of people and displacing two million others.

Boko Haram is thought to have killed around 15,000 people, according to U.S. military figures.

Attacks have spilled over Nigeria's border into neighbouring countries including Cameroon, which has been the target of a stream of suicide bombings in recent months.

Along with Chad, Niger, Nigeria and Benin, Cameroon has contributed troops to an 8,700-strong regional task force dedicated to fighting the group.