A weekend assault by suspected Boko Haram fighters in northern Cameroon killed dozens of people, including soldiers and civilians, officials have said, in one of the deadliest attacks by the group in the country.

Cameroon’s defence ministry said that “more than 300 heavily armed Boko Haram” fighters attacked military positions on Darak, an island near Lake Chad in Cameroon’s Far North region some 1,000km from the capital, Yaounde.

The toll, which has been revised several times since the attack, was put at 24 dead, of which 16 were soldiers and eight civilians. The ministry said 84 fighters were killed and eight taken into custody.

Separately, a military source told the AFP news agency that the fighters had killed at least 37 people.

“As of today, we have 21 military and 16 civilian fatalities,” the source said. Another security source told AFP that about 40 attackers had been captured.

Boko Haram has led a decade-long armed campaign to establish an Islamic caliphate in Nigeria‘s northeast.

The violence, which has cost the lives of some 30,000 people and displaced millions, has frequently spilled over into neighbouring Cameroon, Niger and Chad.

A multinational task force, headquartered in the Chadian capital Ndjamena, had been formed to fight the group, pulling troops from Benin, Cameroon, Chad, Niger and Nigeria.

Cameroon’s armed forces are also grappling with an armed revolt by separatists in two English-speaking regions in the west of the country.

According to the International Crisis Group think-tank, 1,850 people have been killed in the domestic fighting, while more than 530,000 people have been forced from their homes, according to UN figures.