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.

Military involvement by other African nations in the fight against the insurgents stands to grow even bigger. 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 and the European Union were attending, along with senior officials from the U.N. peacekeeping department.

Earlier, Bakary told The Associated Press that some 800 Boko Haram fighters were rampaging through the frontier town of Fotokol, located in a thin northern panhandle of the West African nation.

They have "burned churches, mosques and villages and slaughtered youth who resisted joining them," he said, adding that the insurgents also stole livestock and food. Schools were also being targeted by the insurgents, whose nickname means "Western education is forbidden" in the Hausa language.

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 were killed 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.

The Boko Haram fighters are believed to have crossed into Cameroon from nearby Gamboru, a Nigerian border town that had been an extremist stronghold since November.

Gamboru was retaken earlier this week and the fighters driven out amid Chadian and Nigerian airstrikes supported by Chadian ground troops.

French jets also were flying over the area 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 air base in N'Djamena, the capital of Chad, which will lead the multinational force. N'Djamena lies on the eastern edge of Cameroon's panhandle, near the conflict zone.

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 other world powers, saying: "France can't resolve all the conflicts in the world."

"Do your work. Don't give lectures. Take action." France previously took the forefront in attacking al-Qaida-linked militants that controlled northern Mali, France's former colony, in 2013 and ousting the insurgents from the main cities. Battle-hardened troops from Chad also took part in the operations against the Islamic militants.

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

Relations between Washington and Nigeria have been strained because the United States has refused to sell Nigeria helicopter gunships and other military weaponry that U.S. law prohibits from being sold to countries whose militaries are accused of gross human rights abuses.

The Nigerian military is accused of killing thousands of civilians under state of emergency powers that were declared to curb Boko Haram's rebellion.

Nigeria, Africa's most populous nation, has the continent's biggest economy and is its top oil producer, with most reserves being in the southwest of the country and offshore.

International concern has grown as Boko Haram has increased the tempo and ferocity of its attacks just as Nigeria is preparing for presidential and legislative elections on February 14.

Some 10,000 people were killed in Boko Haram violence last year compared to 2,000 in the first four years of Nigeria's Islamic uprising, according to the Council on Foreign Relations.