The London-based rights group Amnesty International is seeking an investigation into the alleged deaths of hundreds of people in detention facilities during a crackdown on Muslim groups in Nigeria, saying it has evidence.
In a report on Tuesday, the organisation said that "credible information" from a senior Nigerian army officer indicated that more than 950 people suspected of having links to Boko Haram died in military custody in the first six months of this year.
Boko Haram, an armed group, wants to topple the Nigerian government and impose an Islamic state, and has been responsible for thousands of deaths.
Amnesty International said prisoners had been suffocated, starved and subjected to extra-judicial killings in the army-led operation in the country's northeast.
It said senior Ministry of Defence officials had not responded to written details about soldiers on April 19 depositing 60 bodies at the main hospital mortuary in Damaturu, the Yobe state capital, claiming they were killed in a shootout.
But a source told Amnesty International they were detainees taken from their cells and shot.
It said other detainees have suffocated and starved to death in horrendous conditions.
The Nigerian army has consistently rejected accusations of human-rights abuses.