Niger’s national human rights commission has accused the army of executing dozens of civilians during counterinsurgency operations.
It said it had discovered more than 70 bodies in six mass graves in Tillaberi in the north-west of the country, an area affected by jihadist violence.
The killings allegedly happened earlier this year.
One of the investigators said the civilians had been killed with bladed weapons and small arms.
International rights groups have accused the armies of Niger, Mali and Burkina Faso of carrying out dozens of extrajudicial executions during campaigns against jihadists and other armed groups in the Sahel region.
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Niger’s National Commission on Human Rights was investigating allegations that 102 civilians had gone missing in the troubled region between 27 March and 2 April after an army operation.
“There have indeed been executions of unarmed civilians and the mission discovered at least 71 bodies in six mass graves,” said Abdoulaye Seydou, the president of the Pan-African Network for Peace, Democracy and Development, which took part in the investigation.
“It is elements of the Defence and Security Forces (FDS) which are responsible for these summary and extrajudicial executions,” he added.
But Mr Seydou said it was not possible to say whether top levels of the army were responsible.
There has been no response to the claim from the Niger authorities.