The attack occurred during the morning service of a Catholic and Baptist church on Sunday, Reverend Danlami Gajere, CAN chairman for Kasuwan Magani ward in Kaduna state, told Reuters by phone.
The state police spokesperson and Kaduna's commissioner for internal security did not immediately respond to a request for comment.
Two weeks ago, gunmen wielding AK-47 rifles and explosives attacked St Francis Catholic Church in Owo town, killing 40 people. The government suspect insurgent group Islamic State West Africa Province (ISWAP). But ISWAP has not claimed responsibility for the attack.
Armed gangs are rife across Nigeria's northwest where they rob or kidnap for ransom, and violence has been increasing, where thinly stretched security forces often fail to stop the attacks.