Human Rights Watch on Wednesday raised alarms over Nigeria’s mass trials of alleged jihadists, saying many convictions were secured with minimal evidence and possibly under duress.

Africa’s largest country has been battling a jihadist insurgency since 2009, with both militants and security forces accused of serious rights abuses.

But mass trials involving hundreds of alleged jihadists or their supporters speeding through the courts — sometimes after defendants spend years in pre-trial detention — “continue to target primarily low-level suspects and raise significant fair trial concerns” the rights group said in a new report.

Human Rights Watch observed court appearances in April, where more than 500 defendants were brought to the Federal High Court in Abuja in just a few days, and again in June.

The June trials, of some 600 defendants, marked the tenth phase of a series of mass trials that the government has said is necessary to combat “terrorism” amid a backlogged court system.