A leading rights group says Boko Haram militants have killed more than 2,000 civilians in Nigeria this year, nearly three-fourths of them in the northern state of Borno.
Human Rights Watch says the militants carried out nearly 100 attacks during the first six months of the year, including bomb blasts that targeted marketplaces, a brothel, a technical college and two public viewings of soccer matches.
The rights group released its findings on Tuesday, a day after witnesses said suspected Boko Haram militants killed at least 26 people during a raid in the Borno state village of Dille.
Villagers say gunmen fired shots at civilians and burned homes and churches during the attack, late Sunday, in the mostly Christian village.
There was no immediate confirmation from the Nigerian government. But witnesses say military warplanes opened fire to repel the attackers.
Boko Haram has been battling the Nigerian government since 2009. The Human Rights Watch director for West Africa, Corinne Dufka, says in addition to murders, Boko Haram is responsible for rapes, torture and other atrocities.
"We believe that the nature of these attacks, the similarity, the organized nature in which they are being committed suggest that they really are crimes against humanity," she said.
Human Rights Watch said it compiled its figures about the attacks by analyzing credible media reports and the findings of human rights organizations, as well as interviewing witnesses and victims of attacks.
Boko Haram stepped up its attacks after the government imposed a state of emergency in Borno, Yobe and Adamawa states last year.
The group has said it wants to establish a strict Islamic state in northern Nigeria. The group has also kidnapped civilians, including more than 200 girls who were attending school in the northern town of Chibok.
On Tuesday, Nigerian police said they had arrested a senior Boko Haram commander, known as the "Chief Butcher." Authorities say Mohammed Zakari was taken into custody during a counter-insurgency sweep through northern Nigeria.
Police say Zakari is linked to the deaths of seven people, including women and children.