Gunmen have raided an artisanal gold mining site in Nigeria’s northwestern state of Zamfara and killed at least 19 people, a mining union official and Amnesty International told AFP on Friday.

Yahaya Adamu Gobirawa, the union official, said that on Thursday “bandits attacked the mining site at noon and killed 19 people, including five vigilantes providing security to the miners”, while Nigeria’s country director at Amnesty International, Isa Sanusi, gave a toll of 20 based on multiple sources.

“The bandits went directly to the goldmine and killed instantly 14 miners, but more bodies were later discovered, including those who died later as a result of bleeding,” said Sanusi.

Police did not confirm the attack, saying they were still checking for information on the assault, which occurred in Gobirawar Chali village in Zamfara state’s Maru local government area.

Zamfara is one of several states in northwestern and central Nigeria terrorised by criminal gangs — called bandits by locals.

They raid villages and kill and abduct residents across the country’s rural hinterlands, where government presence, infrastructure and security have long been scarce.

Gobirawa described the attack as “unprovoked” and said that the assailants first raided the site Tuesday “but were repelled”.

But on Thursday, “they returned in much larger numbers and overwhelmed the miners and the vigilantes”, he said. “The bandits were better armed because they were using heavy guns”.

He said the mine was recently opened just outside the village and “we believe they attacked the site because they were not involved in running it”.

Last year, the Zamfara state government set up the Zamfara Community Guards, comprising 5,200 personnel to secure communities.