Clashes between security forces and militants in the northeastern city of Bauchi killed more than 50 Nigerians, residents and hospital sources said.
The fighting began early on Sunday when around 70 militants armed with guns and explosives attacked a local police station in retaliation for the arrest of their leaders.
Police and soldiers repelled the attack and then raided neighborhoods to arrest those responsible. Hospital sources and residents said more than 50 people were killed in the fighting, Reuters reports.
However, Emmanuel Ojukwu, a police spokesman, could not give confirm the death toll, saying only that the number of dead was in the dozens, Aljazeera.net reports.
The police spokesman, Mohammed Barau, said the situation had been brought under control and that more than 150 people had been arrested.
One gang member, who gave his name as Abdullah, told Reuters the group had retaliated because authorities had been arresting its leaders.
The man was also quoted as saying that the group wanted to "clean the [Nigerian] system which is polluted by Western education and uphold Sharia all over the country".
In the local Hausa language Boko Haram means "Western education prohibited".
People in Bauchi say it is a Muslim sect that has been operating for months and recruiting young men, BBC News reports.
The police spokesman said the group had been “under surveillance” for a number of months. He said that during Sunday’s attack “policemen, in self-defense, protected their lives.” He said no police officers were killed, The New York Times reports.