Thirty-seven suspected illegal miners have died while in the custody of the Nigeria Security and Civil Defence Corps in Niger State, triggering investigations by security authorities into the circumstances surrounding the deaths.

Niger State Governor Mohammed Umaru Bago confirmed the death toll on Thursday, September 17, after the detainees were found dead at an NSCDC facility in Minna.

The victims were among scores of suspects arrested during anti-illegal mining operations conducted by the NSCDC in the M.I. Wushishi and Lukoto areas of Niger State on September 15 and 16.

The Niger State Command of the NSCDC had initially said the detainees were found dead in the early hours of Thursday following what it described as a suspected disease outbreak.

However, the NSCDC National Headquarters later cautioned that the cause of death had not been established and said any suggestion that a particular disease was responsible remained subject to medical and laboratory confirmation.

The remains of the deceased have been deposited at the General Hospital in Minna for medical examination to determine the actual cause of death.

NSCDC Commandant-General Ahmed Abubakar Audi has also ordered the constitution of a high-powered investigative team led by the Deputy Commandant-General in charge of Intelligence and Investigation.

According to the Corps, the investigation will examine the condition of the suspects when they were arrested, the duration and conditions of their detention, the medical attention available to them and other circumstances surrounding their deaths.

The Niger State Police Command has opened a separate investigation into the incident.

Commissioner of Police Adamu Abdullahi Elleman directed the Deputy Commissioner of Police in charge of the State Criminal Investigation Department in Minna to lead the police inquiry.

Police have also asked relatives of the deceased and members of the public with information that could assist investigators to approach the SCID.

Governor Bago subsequently declared three days of mourning for the victims, while the state government cancelled a political campaign rally scheduled to hold in Minna on Saturday.

The deaths have generated questions over conditions inside the detention facility.

A survivor quoted by the Associated Press alleged that the suspects had been held in an overcrowded space with inadequate ventilation and struggled to breathe before some detainees died.

That account has not yet been established as the official cause of death.

The NSCDC has said it will refrain from speculation until medical examinations are completed, while promising that the circumstances surrounding the deaths will be thoroughly investigated.

The Corps said it remained committed to protecting the dignity, safety and fundamental rights of people in its custody while carrying out operations against illegal mining and other threats to Nigeria's critical national assets.

Investigations by the NSCDC, police and medical authorities are expected to determine what caused the deaths and whether failures in detention conditions or other factors contributed to the incident.