Suspected militants from Nigerian Islamist group Boko Haram have kidnapped about 80 people and killed several others in a cross-border attack on villages in neighbouring Cameroon.

Police say the vast majority of those kidnapped are women and children.

During the attacks several people were killed and some houses were burnt to the ground.

They said soldiers intervened and exchanged fire with the raiders for around two hours.

The kidnapping was the biggest in Cameroon by the Islamists who have staged a series of attacks in the country in recent months and escalated their bloody insurgency in their stronghold in north-eastern Nigeria.

This attack is likely revenge for recent comments by Cameroon, criticising Nigeria for not doing enough to combat the insurgency.

The assault was launched after neighbouring Chad deployed troops to combat Boko Haram both in Cameroon and Nigeria.

Chadian troops are seeking to recapture the Nigerian city of Baga, on the shores of Lake Chad, which straddles the borders of Chad, Nigeria, Niger and Cameroon and which fell to the Islamists early this month.

Boko Haram massacre

Satellite pictures released by Amnesty International and Human Rights Watch showed widespread destruction with around 3,700 buildings in Baga and nearby Doron Baga damaged or destroyed.

Amnesty International said as many as 2,000 civilians may have been massacred, but Nigeria's army objected to the "sensational" claims and said the death toll in Baga was about 150.

Some 400 Chadian army vehicles arrived in the Cameroonian border town of Kousseri on Saturday, and Chadian president Idriss Deby said they were "operational" as of Sunday.

Boko Haram last Monday launched an offensive against a Cameroonian military base in Kolofata, also in the far north of the country, in which 143 "terrorists" and one Cameroonian soldier were killed, according to Cameroon.

Boko Haram seized control of many towns and villages in north-east Nigeria, and has begun threatening some of the country's neighbours.

In April, Boko Haram kidnapped more than 200 girls from a boarding school in Nigeria, most of them have not been seen since.

The African Union will meet this week to discuss a plan to deal permanently with Boko Haram.