MAIDUGURI: At least 50 people were killed by militants on Sunday around the town of Rann in Nigeria's Borno state, in the country's northeastern tip near the border with Cameroon, witnesses told Reuters by phone on Monday.

Since 2009, Nigeria's northeast and Borno state in particular have been the centre of an insurgency led by the militant Islamist group Boko Haram. Millions have been displaced and some 350,000 people have died from attacks and the subsequent humanitarian crisis, according to the United Nations.

Over time, Boko Haram has split with an active offshoot called Islamic State West Africa Province also claiming responsibility for attacks in the west African country.

Local residents blamed the latest attack on Boko Haram. Army spokesman Brigadier General Onyema Nwachukwu did not immediately respond to a request for comment.

"We are all in pain over the killing of our innocent people who were working on their farmland. ... We buried 50 people today in Rann. They were clearing their farmlands ahead of the rainy season, while others went for firewood," Harun Tom, a local farmer, said.

Agid Muhammad, a farmer who recently returned to Rann after living in an internally displaced-persons camp, described a scene of carnage.

"A large number of Boko Haram on motorcycles armed with guns and machetes surrounded our people who were working on their farms and held them hostages before killing them one by one," Muhammad said, adding that his uncle was still missing.

"They were tied with rope and slaughtered. As I'm speaking to you, many people aren't accounted for."