Authorities in Nigeria say at least 68 people have been killed in fighting between security forces and members of a radical Muslim sect in the north.
A military spokesman said Boko Haram began clashing with security forces Thursday in the cities of Damaturu and Maiduguri, where witnesses have reported hearing gunshots and explosions.
A purported Boko Haram spokesman says the group launched attacks in the cities to avenge the killing of Boko Haram members killed by the security forces in 2009.
The dead include four security agents killed by a roadside bomb Thursday in Damaturu.
Boko Haram has been blamed for dozens of attacks over the past year, as part of a campaign to implement strict Sharia law across the central African country's northern sector.
The shadowy group has claimed responsibility for only some of the attacks, including a suicide bombing at a United Nations building in the capital, Abuja, that left at least two dozen people dead.