Boko Haram affected areas

Researchers say Boko Haram might have thousands more fighters than estimated by intelligence services. Their pockets are lined with cash, thanks to bank robberies and looting in the towns that fall under their control. They also have a supply of arms stolen from the Nigerian military, and some that come all the way from Libya through the Sahel, reportedly linked to other radical armed groups.

France has sent military advisers to Niger's southern border with Nigeria to help coordinate military action by regional powers fighting the Islamist group Boko Haram, a French army official said on Thursday.

French military aircraft are carrying out surveillance missions to help countries bordering Nigeria tackle Boko Haram militants, officials said on Tuesday, amid efforts by African countries to coordinate a response to the threat posed by the group.

The Nigerian militant group Boko Haram is reported to have killed more than 70 people in a cross-border raid into Cameroon.

Chadian troops have entered Nigeria to join the battle against militant Islamist group Boko Haram. Armoured vehicles and infantry crossed a bridge from Cameroon following air strikes and mortar attacks on Boko Haram positions, officials say.

The African Union has endorsed a West African plan to set up a regional task force of 7,500 to fight Islamist Boko Haram militants, a senior official said on Thursday, a vital step towards securing U.N. Security Council backing.