Nigerian President Muhammadu Buhari has condemned the killing of "tens" of villagers in restive northwestern Zamfara state and ordered security forces to hunt down the perpetrators.
Local residents said as many as 60 people could have been killed in Wednesday's rampage in about a dozen villages in the state but only nine bodies had been recovered.
Police and government officials could not immediately confirm the death toll.
Heavily-armed criminal gangs known locally as "bandits" have become a growing security challenge in northwest Nigeria, ransacking villages and carrying out mass abductions for ransom.
In a statement late Thursday, Buhari said "such wanton disregard for life will be brought to an end sooner than later."
He ordered security forces to rid the region of "frequent and horrifying bandit activities."
"The violence against poor villagers who are struggling with poverty and other severe economic challenges is not going to be tolerated by this administration," he said.
"Let's not give these criminals any opportunity to succeed by taking the war to their own camps and stop them in their tracks before they even have the time to respond under our massive fire power."
Local residents said motorcycle-riding gunmen stormed 13 villages in Magami district of Zamfara state on Wednesday, shooting residents, looting and burning homes.
- Gunmen on motorbikes -
The villages included Kangon Farimana, Ruwan Dawa, Madaba, Arzikin Da, Mairvairai, Gidan Maza, Unguwa Malam and Katohin.
"These are neighbouring villages and the bandits rode in motorcycles, shooting anyone at sight," resident Halliru Bala told AFP.
"Most of those killed were volunteers who mobilised to help fend off the attacks," he said.
"We buried nine people yesterday (Wednesday) here in Magami but we are still looking for 51 others," he said.
"We believe they were killed and their bodies are lying in the villages which have been deserted following the attacks."
Another resident, Babangida Ilu said villagers had fled the communities.
"We are still afraid to go into our villages to pick the dead because the bandits are still around nearby bushes and would attack whoever goes back," he said.
"Only nine out of the 60 people we lost in the attacks were recovered and buried. The rest are still scattered in the villages. We are afraid to go there because of the bandits."
Ilu said the gunmen looted food supplies and burnt homes during the attacks.
"The bandits went from village to village on a killing spree which made people to flee," said Altine Musa, another resident.
Zamfara has been the hardest hit by bandits in the volatile northwest despite a government offer of amnesty in exchange for renouncing violence and surrendering their weapons.
Nigerian police said on Tuesday they had killed 30 gunmen after the criminals raided some villages and slaughtered 10 people in the state.
Criminal gangs have recently targeted schools and colleges for kidnapping attacks, hoping to get ransom payments out of the authorities.
On Tuesday, some students were seized from private Greenfield University in Kaduna state while a member of staff was killed, in the fifth such attack since December.