Thirty-seven people accused of illegal mining in north-central Nigeria have died in custody, official say.
Police have set up an investigation into the deaths, which the Nigerian Security and Civil Defence Corps (NSCDC) blamed on an apparent disease outbreak.
However, an intelligence report shared with AFP news agency suggested the group had died because of overcrowding and poor ventilation inside the detention facility in Niger state.
The deaths have sparked disturbances including attacks on public buildings, and a 24-hour curfew has been put in place in the state capital, Minna, as a result.
On Tuesday, a group of young men were arrested for suspected illegal mining near Borgu – a part of Niger state known for small-scale gold mining.
Two days later, 37 people were found dead inside the detention centre run by the NSCDC – responsible for protecting critical infrastructure and tackling crimes including illegal mining.
NSCDC spokesperson Babawale Afolabi said more than 50 people had been arrested, and they had not been charged because profiling and documentation were still under way before the deaths.
The father of one of those detained said relatives went to the NSCDC office seeking their release but were repeatedly told to return later.
“Unfortunately, the following day we got the news that our children had died,” he added.
Abdullahi Dalhatu told the BBC: “We believe they suffocated because there was no ventilation.”
He said his son had survived because he was near a small window. “His friend slumped and fainted, and many others also collapsed.”
His son described how detainees fainted in the heat of the overcrowded and poorly ventilated cell, his father said.
He said detainees repeatedly knocked on the door for help but nobody opened it.
The BBC has not independently verified his account.
One father told Nigerian media that his son had appeared healthy when relatives took him food the day before his death and called for an independent post-mortem examination.
