Residents of ​a city in central Nigeria took to the streets to ‌protest overnight after at least 33 detainees were found dead in the custody of a paramilitary force that raided suspected illegal gold mines.

Reuters filmed 33 bodies laid out ​in a ward at the General Hospital in Minna, the ​capital of Niger State, on Thursday, after they were found ⁠dead in the custody of the Nigeria Security and Civil Defence Corps (NSCDC).

The ​agency said the detainees had been held in raids on suspected illegal ​mines on September 15 to 16 in the Wushishi-Lukoto area west of Minna. It initially said a suspected disease outbreak may have been involved in their deaths, but ​later said the cause of death had not been established and would ​be determined by medical examinations.

Interior Minister Olubunmi Tunji-Ojo ordered the immediate suspension of Niger ‌State's ⁠NSCDC commandant, Suberu Siyaka Aniviye, pending the outcome of a full investigation.

"It is an unfortunate incident, however, a full investigation will be conducted while the commandant under whose watch this happened remains suspended," the Interior Ministry ​said in a statement.

Anger ​over the ⁠deaths sparked protests in Minna on Thursday night, with youths chanting "Justice must be done", according to residents. Some protesters ​also damaged vehicles.

By Friday morning the city was calm, ​but ⁠security forces had been heavily deployed across parts of Minna.

Nigeria has tried for years to curb illegal mining at thousands of informal sites that operate ⁠across the ​country. The authorities say illegal mining damages ​the environment and leads to losses of government revenue.