Updated

A new study indicates that the desire for revenge against Nigeria's heavy-handed military is a leading reason that people join Boko Haram's Islamic extremist group.

Nearly 60 percent of 119 former Boko Haram fighters interviewed in Nigerian rehabilitation camps cited revenge against the military as having a strong, or being the only, influence in their recruitment.

The study published Monday was conducted by Helsinki-based Finn Church Aid and The Network for Religious Peacemakers and South Africa's Vibrand Research.

Separately, Amnesty International has reported some 7,000 people, including babies, have died in military detention linked to the insurgency.

President Muhammadu Buhari has promised to halt military abuses, but they continue.

Overall, an estimated 20,000 people have died in the seven-year Boko Haram uprising.