Gunmen have opened fire on worshippers during a church service in central Nigeria, killing at least 15 people.

Nigerian officials say an unknown number of gunmen stormed the church late Monday near Okene in Kogi state.

Kogi state is in Nigeria's middle belt, where the Muslim-dominated north and the Christian-majority south meet.

There was no immediate claim of responsibility. The Islamic militant group Boko Haram has claimed a series of recent attacks on Christian churches and villages in the region.

Boko Haram says it is fighting to create an Islamic state in northern Nigeria and does not recognize the Nigerian government or the constitution.