Saturday's attack on farmers working in rice fields in the Garin Kwashebe village of Borno state killed at least 110, Edward Kallon, UN humanitarian coordinator in Nigeria, told a news conference on Sunday according to foreign media reports.
Earlier, local media had reported that at least 44 farmers were killed in the attack, with many wounded.
"The incident is the most violent direct attack against innocent civilians this year. I call for the perpetrators of this heinous and senseless act to be brought to justice," said Kallon.
The attackers tied up agricultural labourers working in rice fields and slit their throats near Maiduguri, the capital of Borno state, reports say
Underlining that many women are also believed to have been kidnapped by the terrorists, he called on the Nigerian government to take action regarding the incident.
Nigerian President Muhammadu Buhari condemned the attack, slammed also by Turkey which extended its "sincere condolences" on Sunday to the victims' families and the nation.