Nigerian President Muhammadu Buhari delivers a speech during the Aswan Forum for Sustainable Peace and Development in Aswan, Egypt, Dec. 11, 2019. (Xinhua/Ahmed Gomaa)

Nigeria's President Muhammadu Buhari on Saturday described as "mass murderers" gunmen known locally as "bandits" who killed more than 140 people in multiple raids this week according to residents.

"The latest attacks on innocent people by the bandits is an act of desperation by mass murderers," Buhari said in a statement.

Clashes between herders and farmers over access to land has plagued northwest and central Nigeria for years, with some groups evolving into criminal gangs who now terrorize local communities.

"We buried a total of 143 people killed by the bandits in the attacks," said Balarabe Alhaji, a community leader in one of the affected villages in Zamfara state.

Hundreds of motorcycle-riding gunmen rampaged through ten villages in Anka and Bukkuyum districts on Wednesday through Thursday, shooting residents and looting and burning homes, locals said.

Babandi Hamidu, a resident of Kurfa Danya village said the militants were shooting "anyone on sight."

"More than 140 people were buried across the ten villages and the search for more bodies is ongoing because many people are unaccounted for," Hamidu said. Idi Musa, a resident of another village, Kurfa Danya, said "the death toll is huge. We are talking of around 150 people killed by the bandits."

The bandits also stole "around 2,000 cattle," Musa added. 

Another resident who only gave his first name Babangida gave a similar account.

All four sources said they were present at burials in their respective villages. 

Neither the police nor military have commented on the attacks.

But in his statement Saturday, Buhari said: "Let me reassure these besieged communities and other Nigerians that this government will not abandon them to their fate because we are more than ever determined to get rid of these outlaws."

On Wednesday, the Nigerian government officially labeled bandits as terrorists, to bring tougher sanctions against convicted gunmen, their informants and supporters.