The radical Islamic group Boko Haram, whose name means "Western education is sinful," claimed responsibility for what appeared to have been coordinated attacks.
The deadliest bombing took place near Saint Theresa Catholic Church in Madalla, where worshipers celebrated a Christmas Day mass. Angry youths, furious at the bloodshed, set up burning barricades near the church, prompting police to fire shots into the air.
Another bomb exploded near an evangelical Christian church in the central city of Jos, where clashes between Muslims and Christians are frequent. Officials say a police officer guarding the area was fatally shot around the time of the explosion.
In the northeastern state of Yobe, residents in Gadaka say a bomb blew up near a church during Christmas services. There were no immediate reports of deaths. A fourth attack took place in the Yobe capital of Damaturu, where a car bomb killed three near secret police headquarters.
World leaders condemned the violence. The White House called it senseless terrorism, while a Vatican spokesman said the blasts were acts of "blind hatred." United Nations Secretary-General Ban Ki-moon said "no objective ... can justify" the attacks. British Foreign Secretary William Hague said the bombings were "cowardly" and Italy's Foreign Minister Guido Terzi condemned them as "vile."
Nigeria has struggled with a wave of violence centered in the country's north, where government security forces are battling Boko Haram.
The group has said it wants to establish an Islamic state in northern Nigeria and does not recognize the government or the country's constitution.
The country of 150 million is about evenly divided between Muslims, who mostly live in the north, and Christians who dominate in the south.
Authorities say violence in and around the cities of Maiduguri and Damaturu has killed at least 68 people over the past few days.
Hundreds of others have died this year in bombings and shootings blamed on Boko Haram.
In Jos, thousands of people have died in recurring bouts of Muslim-Christian violence over the past decade. The city sits in Nigeria's Middle Belt, where the mostly Muslim north meets the mainly Christian south.
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