Amnesty International on Wednesday called on Nigerian authorities to investigate unexplained disappearances, as the rights group highlighted a pro-Iranian Shiite religious movement that claims 600 of its members are missing.

“Amnesty International is calling on the Nigerian authorities to investigate all cases of enforced disappearances and bring all those suspected of criminal responsibility to justice,” the group said in a statement.

“According to figures provided by the Islamic Movement of Nigeria (IMN), at least 600 of their members’ whereabouts is not known.”

More than 350 IMN followers, led by firebrand cleric Ibrahim Zakzaky, were killed in clashes with the military in the northern town of Zaria in December 2015.

Trouble started on December 12 of that year when Zakzaky’s supporters refused to allow the chief of army staff’s convoy to pass through the town, sparking violence.

Zakzaky, who was shot and injured leaving him partly paralysed and blind in one eye, remains in protective custody, according to the military.

He has repeatedly been imprisoned for alleged incitement and subversion.

IMN has been in conflict with the Nigerian government for years, seeking to foment an Iranian-style Islamic revolution in the country’s Sunni Muslim-majority north.

Amnesty, marking the International Day of the Disappeared, also hit out at disappearances of young men “often seized by the military after being accused of affiliation to the armed group Boko Haram”.

Amnesty said hundreds of other civilians had disappeared in the restive northeast during the jihadist group’s brutal eight-year insurgency. Many more are being held illegally in “secret detention”, it charged.

“The families of the victims of enforced disappearance have already waited too long for answers,” Amnesty’s statement said. “They deserve justice, truth and reparation now.”

The uprising by Boko Haram, which is seeking to impose hardline Islamic law in Nigeria’s mainly-Muslim north, has claimed the lives of at least 20,000 people and forced some 2.6 million others to flee their homes since 2009. (AFP)