DAKAR, Senegal — More than 100 people have been tortured by Cameroon’s security forces and held incommunicado in the past four years after being accused of having links to the extremist group Boko Haram, according to a report issued Thursday by Amnesty International.

“Detainees were severely beaten with various objects including electric cables, machetes and wooden sticks,” the report said, adding that they were also suspended from poles and subjected to drowning, and that many were deprived of food, water and medical care. In most cases, people were held on little or no evidence.

More than 30 people interviewed said they had witnessed deaths after torture.

Suspects are usually detained after attacks by Boko Haram, whose insurgency has killed more than 20,000 people and displaced millions in Nigeria and nearby countries, including Cameroon.

Boko Haram has killed more than 1,500 civilians in northern Cameroon since 2014, Amnesty said. Cameroon, Chad and Niger all contribute to a multinational force to combat the insurgency.