Three girls recruited as suicide bombers have been killed in Cameroon.

The girls, believed aged between 11 and 15, were killed trying to carry out attacks for Boko Haram extremists, according to Mayo-Sava border region officer Babila Akawa.

Two died when they detonated their explosives after police spotted them crossing the border from Nigeria to Cameroon, Akawa said on Saturday.

Another was killed in the northern border town of Mora as she tried to flee. Two other girls are believed to have escaped.

Cameroonian forces have increased their vigilance after 11 people were killed in twin suicide attacks last week.

Rights group Amnesty International has, however, has accused Cameroonian forces of the arbitrary arrest and torture of ordinary people accused of links to the extremist group.

Boko Haram, the Nigeria-based Sunni fundamentalist group, has killed at least 14,000 people in Nigeria, Chad, Cameroon and Niger.

The group is also known for their kidnapping of dozens of schoolgirls in Nigeria in 2014.