The men attacked the village of Faduma Koloram, in Gubio local government area of Borno state, starting about noon.
They arrived in vehicles and on motorcycles, shooting with AK-47s, razing the village and stealing 1,200 cattle and camels, three sources told Reuters.
A resident, a Civilian Joint Task Force (CJTF) member and a soldier each confirmed the same account.
They said the men attacked because they suspected residents of sharing information on Boko Haram's movements with security authorities.
"It's an unfortunate day for us to witness this," said CJTF fighter Kachallah Bumu. While he said the residents were armed, and had repelled previous attacks, this one caught them off guard.
"They took us unaware and killed our people," he said.
A military spokesman could not be reached for comment.
Boko Haram and its offshoot, West Africa Province (ISWAP) of the Daesh Takfiri terrorist group, have killed thousands and displaced millions in northeastern Nigeria.