Gunmen killed more than 30 gold miners in a remote area of northern Nigeria, police said on Tuesday.
The attackers raided a camp of artisan miners late on Monday in the Maru area in the north-western state of Zamfara, police spokesman Muhammed Shehu said.
The gunmen stole nothing, he said, adding the motive for the attack was unclear.
In March gunmen attacked a camp in the same state, killing one miner in what a police official described as possible conflict between miners.
Nigeria has been trying to attract investment in its nascent mining sector but insecurity and a lack of data has dampened the appetite of foreign firms.