Gunmen attacked a Catholic church in southwestern Nigeria's Ondo state during mass on Sunday, killing several people, local media reported.
A doctor at a hospital in Owo, a town in the state in Nigeria's southwest, told Reuters that "several worshippers were brought in dead".
Funmilayo Ibukun Odunlami, police spokesperson for Ondo state, said "there was an incident today at the Saint Francis Catholic Church in Owo" and police would issue a statement soon.
Local media said gunmen had fired at worshippers and detonated explosives at the church.
Africa's most populous country has witnessed attacks and kidnappings for ransom by armed gangs, mostly in its northwest. Such attacks are rare in southwestern Nigeria.
Ondo state governor, Arakunrin Oluwarotimi Akeredolu said he was heading back to the state from the capital Abuja after the "unprovoked attack and killing of innocent people of Owo."
"We shall commit every available resource to hunt down these assailants and make them pay," he said in a statement.