YAOUNDE, Cameroon — Hundreds of Boko Haram fighters took revenge Thursday on villagers in Cameroon, shooting and burning scores to death and razing mosques and churches after warning Nigeria’s neighbors not to join the battle against the Islamic insurgent group.

France’s president warned that the world was not doing enough to end the wanton killings by the militants, who have waged a campaign of terror in a broad swath of northeastern Nigeria, where they declared an Islamic caliphate in August.

At least 91 villagers were killed and more than 500 were wounded in the northern Cameroon town of Fotokol on the border with Nigeria, where fighting began Wednesday and continued Thursday, Cameroonian officials said.

While Boko Haram has previously carried out attacks in Cameroon, the latest bloodshed came after the group warned Nigeria’s neighbors against uniting against it.

Cameroon and Chad joined Nigeria in launching an air and ground offensive against the insurgents on at least two fronts this week.

Last week, African leaders authorized a 7,500-strong force to fight the Islamic extremists.