Cameroon's army, with backing from a regional anti-Boko Haram task force, has killed at least 100 fighters from the Islamist militant group and freed 900 people it held hostage, the army said on Wednesday.

"In the course of this operation, at least 100 members of Boko Haram were killed. Nine hundred hostages detained by Boko Haram were freed," said army spokesman Colonel Didier Badjeck.

The defence ministry also cited the same figures in a brief statement on state television.

Boko Haram has expanded attacks into Cameroon, Chad and Niger — all countries contributing troops to a regional force intended to wipe out the extremists.

Earlier, the governor of Cameroon's Far North province said two teen female suicide bombers had detonated explosives in the border town of Waza, killing at least six people.

Midjiyawa Bakary said the attackers came from Nigeria and a third suicide bomber was killed before she attacked.

Senior military official Col. Jacob Kodji on Wednesday said Nigeria's Boko Haram extremists have been using teenage suicide bombers and planting land mines.

He said two Cameroonian soldiers were killed Monday by a land mine planted by militants in the village of Gangse in northern Cameroon.

With files from The Associated Press