The authorities have introduced a round-the-clock curfew.
The authorities believe that, most likely, the explosions were set off by the terrorist Moslem organization Boko Haram.
Nigeria church blasts kill 19, spark reprisals
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.
First, a suicide bomber drove a blue Honda Civic into Ekwa Church, its pastor told a Reuters cameraman at the scene.
"Three people are confirmed killed. Others have been taken to hospital for treatment," said Reverend Nathan Waziri.
The second suicide car bombing was at Kings Catholic Church, killing 10 people, said Bishop of Zaria George Dogo who was giving a service in the church when it was attacked.
Suicide bombers in a Toyota saloon then hit Shalom Church in the state's main city of Kaduna, killing six people. The military said the dead included an army sergeant.
Reuters, TASS
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Two car bombs blasted near bailiff service building in Makhachkala, there are casualties - source