ZARIA, Nigeria - Suicide car bombers attacked three churches in northern Nigeria on Sunday, killing at least 19 people and wounding dozens, and triggering retaliatory attacks by Christian youths who dragged Muslims from cars and killed them, officials and witnesses said.

There was no immediate claim of responsibility for the bombings but Islamist group Boko Haram has often attacked church services in Nigeria, Africa's most populous country, split roughly evenly between Christians and Muslims.

The violence stoked fears of wider sectarian conflict in Nigeria, an OPEC member and Africa's top oil producer where the Christian Association of Kano, northern Nigeria's main city, called the bombings "a clear invitation to religious war".

Last Sunday, militants attacked two churches in Nigeria, spraying the congregation of one with bullets, killing at least one person, and blowing up a car in a suicide bombing at the other, wounding 41. Boko Haram claimed responsibility.

In the latest violence, the first two blasts rocked churches in the town of Zaria within minutes of each other.

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