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.

Meanwhile, 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.

Military involvement by other African nations is expected to increase. African Union officials met Thursday to finalize plans for a multinational force to attack Boko Haram, though its deployment could be delayed by funding issues.

Last week, African leaders authorized a 7,500-strong force to fight the Islamic extremists, including pledges of a battalion each from Nigeria and its four neighbors, Cameroon, Chad, Niger, and Benin.

"We consider Boko Haram to be a cancer, and if the international community does not focus its mind on this disease it will spread not only in Central Africa but other regions, all over the continent," Cameroon’s Information Minister Issa Tchiroma Bakary said at the start of the three-day meeting in Yaounde, Cameroon’s capital.

Officials from the United States, France, Russia, Britain, the United Nations, and European Union attended this meeting.

Hundreds of Boko Haram fighters were killed Wednesday, according to Cameroon’s defense minister, Edgard Alain Mebe Ngo, who said 13 Chadian and six Cameroonian troops also died in the fighting. There was no way to independently confirm the account.

At least 91 civilians were killed, Ngo said, adding that most of the 500 wounded were trapped and could not be taken to hospitals. French jets were flying over the area of battle in Cameroon to provide intelligence, French defense officials in Paris said.

President Francois Hollande said France was supporting the operation with logistics, including providing fuel and sometimes munitions, though he stopped short of saying whether France would participate in military action. France has a big base in N’Djamena, the capital of Chad, which will lead the multinational force.

The French leader told a Paris news conference that France supports African forces fighting what he called a ‘‘terrorist sect’’ that has carried out ‘‘horrible massacres.’’

He issued a stern call to world powers, saying, "France can’t resolve all the conflicts in the world. Do your work. Don’t give lectures. Take action."

At the Yaounde meeting, US Ambassador Michael S. Hoza said the United States would help in the fight against Boko Haram, though he did not provide details.