Gunmen attacked a cattle market in remote northeastern Nigeria overnight, killing up to 56 people, according to police and hospital sources.
It was not clear who was behind the attack last night in the town of Potiskum, in Yobe state, which has been an occasional target for militant Islamist sect Boko Haram.
Witness Mama Yusuf, a retired civil servant, said there were dead bodies on the ground. "I saw dead bodies all around the place and the emergency services taking people to hospitals. I don't know how many died, but I saw deaths," he said.
Boko Haram has been fighting a low-level insurgency for more than two years and has become the main security threat facing Africa's top oil producer. It usually targets police or authority figures but civilians have increasingly borne the brunt of its attacks.
Sometimes violence in Nigeria, especially in parts of the north or the volatile Middle Belt - where the largely Christian south and Muslim north meet - is driven by ethnic rivalry over land and resources that has little to do with the insurgency.
Boko Haram, which wants to impose an Islamic state on Nigeria's mixed population of Muslims and Christians, has been blamed for hundreds of killings since its uprising against the government began in 2009.A spate of attacks in the past few days, including one against Christians in the north that killed 19 people on Sunday,
have dampened hopes that tighter security had significantly reduced the sect's capability.
Nigerian forces killed the suspected mastermind of Sunday's attack on Christian worshippers, in a raid in the main northern city of Kano on Tuesday that resulted in a gun battle lasting several hours.