Nigerian army spokesman Maj. Gen. Raphael Isa, in an interview with the BBC, blamed the Islamist group Boko Haram.
The group, which wants to institute strict Shariah law in the country, has been accused of a number of attacks in the northeast of the country, with thousands of people fleeing their homes in Maiduguri and other cities attacked by the group.
Boko Haram is suspected of targeting a number of churches on Christmas Day with bombings that killed at least 42 people.
Ongoing sectarian violence has plagued Nigeria, divided between a largely Muslim north and a mainly Christian south.
Nigeria's main Christian group has warned that the country's Christians may have to defend themselves if the security forces cannot protect them.