"Kano is still in shock," Bishop John Namaza Niyiring of Kano, Nigeria's second-largest city, told Fides. "The coordinated series of attacks in different parts of the city lasted about three hours."

Bishop Niyiring told Fides that the attackers had exploded bombs in various government and law-enforcement buildings, and subsequently shot randomly at people nearby. Some church buildings were damaged, but no priests or religious were reported among victims of the violence, he said.

"But we have news that some of our parishioners are among the victims," the bishop said.

Many southern Nigerians living in the North were heading home, while northerners resident in the south of the country were returning to their places of origin, "for fear of reprisals," Archbishop Kaigama told Fides.

In a letter to journalists reported by the Associated Press, the group said the attacks were retribution for the arrests and killings of some of its members.

The name Boko Haram, in the Hausa language, means "Western education is sacrilege."