At least 140 people were killed by gunmen known in Nigeria as "bandits" in several raids this week in the northwest of the country, residents told AFP Saturday.

No confirmation was issued from any official authority.

Criminal gangs have been troubling Northwest and central Nigeria for years, but violence has expanded today. On Wednesday, bandits were labeled officially by the Nigerian government as terrorists.

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

According to locals, hundreds of motorcycles ridden by gunmen on Wednesday and Thursday rampaged through ten villages in Anka and Bukkuyum districts, and engaged in several violent acts such as firing at residents, burgling, and burning homes, locals said.

A resident of Kurfa Danya village said they were shooting "anyone on sight".

"More than 140 people were buried across the ten villages and search for more bodies is ongoing because many people are unaccounted for," he 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."

Despite this huge death toll and these violent attacks against the citizens, officials have not yet commented.