"Members of Boko Haram and other groups and entities, if judged to have committed widespread or systematic attacks against a civilian population ... (could be) guilty of crimes against humanity," said Cecile Pouilly, spokeswoman for the UN High Commissioner for Human Rights.
The Islamist insurgents have killed dozens of people over recent days in restive northeast Nigeria, first storming a town on motorbikes and pick-up trucks and then carrying out highway ambushes.
Boko Haram gunmen were blamed for Saturday's slaying of more than 30 people, including the groom, when a wedding convoy was halted on a road near the border with Cameroon.
Pouilly called the wedding convoy "atrocious" and condemned Boko Haram's campaign of "cowardly attacks" against civilians, politicians, members of government institutions, foreigner and the security forces.
In May, Nigerian President Goodluck Jonathan declared a state of emergency across the northeast and launched an offensive aimed at crushing at the Islamists' four-year uprising.
The conflict has claimed thousands of lives since 2009 in Africa's most populous country and top oil producer.
Besides condemning the Islamists' bloody campaign, human rights groups have also slammed government troops for killing civilians and for other violations in the battle zone.
"We are also following up closely with the Nigerian authorities allegations of abuses and human rights violations which may have been committed by security forces when conducting operations," said Pouilly.
She noted that the Nigerian military was in the process of finalising a report on people detained in connection with the insurgency, and urged the government to disclose its findings.
"We also call on the Nigerian government to ensure that security forces act in conformity with the law and avoid excessive use of force when conducting operations," she added.
AFP