The bodies of at least 180 men have been found in mass graves in northern Burkina Faso, according to a report by Human Rights Watch.
The graves were found in a region where government forces are fighting a jihadist insurgency.
The men had been buried under bridges, in fields and along major roads near the town of Djibo in groups of up to 20.
Human Rights Watch said there was evidence they were victims of extrajudicial killings by the army.
The group has urged the government to find out who turned the area into what it called a "killing field".
Defence minister Moumina Cheriff Sy suggested militant groups wearing stolen army uniforms might be to blame.
The government has said it will investigate the claims.