A Nigerian military spokesman says explosions and gunfire inside a University theatre used for Christian services in Kano, in northern Nigeria, has resulted in several casualties.
The official said there are casualties but he did not immediately have a count of the injured or dead.
There has been no immediate claim of responsibility, but the terrorist group Boko Haram has targeted Nigerian Christians in the past.
Last Christmas, at least four bomb blasts killed 39 people, including dozens at a Catholic church near Abuja.
The radical Islamic group Boko Haram, whose name means “Western education is sinful,” claimed responsibility for what appeared to have been coordinated attacks.
The group has said it wants to establish an Islamic state in northern Nigeria and does not recognize the government or the country's constitution.
Nigeria's population of 150 million is about evenly divided between Muslims, who mostly live in the north, and Christians who dominate in the south.
Authorities say violence in and around the cities of Maiduguri and Damaturu has killed at least 68 people over the past few days.
Hundreds of others died last year in bombings and shootings blamed on Boko Haram.