Security forces opened fire in a city in central Nigeria on Friday as hundreds of people took to the streets to protest against the deaths of 37 detainees in the custody of a paramilitary force, witnesses said.

The victims were found dead on Thursday in the cells of the Nigeria Security and Civil Defence Corps (NSCDC), which had raided suspected illegal gold mines and locked up dozens of miners in Minna, the capital of Niger State.  

The government has promised an investigation into the deaths and suspended some senior officials but anger over the incident led to clashes overnight and into Friday. 

A Reuters witness saw security forces fire live rounds as protesters - some armed with sticks, machetes and traditional hunting rifles - called for justice. Some protesters tried to set fire to government buildings in the Tunga neighbourhood. 

"We are not thieves - we are simply seeking a way to make a living by mining," Yusuf Auwal, a miner who joined the protesters, told Reuters. 

At least one body lay on the streets. Soldiers and police officers patrolled Minna to try to restore order.

INVESTIGATION PROMISED, BODIES ALREADY BURIED

The NSCDC 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.

The victims were buried late on Thursday in accordance with Islamic tradition, raising questions about if or how authorities would carry out further forensic examinations to determine the cause of death. 

"WE WILL NOT FORGIVE THEM"

The mother of one of the detainees, Shafa'atu Suleiman, told Reuters outside the hospital on Thursday that she had visited her son Abdullahi in detention and found him in a cramped NSCDC cell, before later learning that he had died. 

Officials had refused to allow relatives to deliver food to the detainees and demanded 100 000 naira ($75) for them to be freed, she said.

"This is injustice. We will not forgive them."

NSCDC officials did not respond to multiple requests for comment on her accusations.

Nigeria has tried for years to curb unauthorised 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.