A bomb was thrown into an Arabic school in mainly Christian southern Nigeria, wounding at least seven, police said Wednesday, after Christmas attacks sparked fears of sectarian violence in the country.

"A locally made low-capacity explosive was thrown into an Arabic school in Sapele at 10:00 pm yesterday," said state police spokesman Charles Mouka.

Christian shops were burnt and hundreds of residents sought to flee one violence-torn city in Nigeria's northeast, residents said Monday, after deadly Christmas attacks shook the country.

In the northeastern city of Potiskum, residents and a police source said about 30 Christian shops burned on Sunday night, while a supermarket and the home of a local Christian leader were also set ablaze.

U.N. Secretary General Ban Ki-moon has strongly condemned the attacks targeting Christian churches in Nigeria and called for an end to violence there.

"The secretary general expresses his sympathy and condolences to the people of Nigeria and to the bereaved families who have lost loved ones," a spokesman for Ban said Sunday.

Bomb attacks on churches during Christmas services and a suicide blast killed at least 35 people in Nigeria on Sunday amid spiraling violence claimed by Islamists.

A purported spokesman for Islamist group Boko Haram claimed responsibility for a bombing of the church outside the Nigerian capital and other violence in recent days that has stoked fear and anger in Africa's most populous nation.

A wave of attacks in northern Nigeria attributed to a radical Islamist group may have killed up to 100 people, police and a local rights group said Saturday.

"From reports I have been receiving from Damaturu, up to 100 people could have been killed," a senior police source in the region told Agence France Presse, while Chidi Odinkalu, head of the Open Society Justice Initiative, gave a figure of 69-100.

Unrest in three northeastern Nigerian cities has left at least six people dead, an official said Friday, after gunfire and explosions rocked the region hit by violence blamed on Islamists.

The unrest broke out in the cities of Maiduguri, Damaturu and Potiskum on Thursday. More gunfire was heard in Damaturu on Friday morning, but details were unclear.

Nigerian officials said they have launched a broadcast satellite into orbit to replace one that was lost in space.

Project manager Abdulrahman Adejah said Monday on state-run television that NIGCOMSAT-1R launched successfully from a Chinese launch pad.

Gunmen have killed a policeman in the northern Nigerian city of Kano, a day after three soldiers died in an attack on a military-run school, police said Saturday.

The gunmen opened fire on a police checkpoint on the outskirts of the city late Friday, resulting in a shootout which left one policeman dead and another seriously wounded, Kano state police spokesman Magaji Majia told Agence France Presse.

Gunmen have attacked a military-run secondary school in northern Nigeria, an air force official said Friday, reporting two officers wounded, though a doctor said four were killed.

"There was an attack on the air force comprehensive school by unknown gunmen," the air force official said on condition of anonymity. The incident late Thursday at the boarding school outside the city of Kano.

An Italian construction worker kidnapped in Nigeria's main oil region has been freed after being held for a day and following a ransom demand of more than $700,000, officials said Thursday.

"He was released on the 10th of December," said police spokesman Eguavoen Emokpae, adding he had been kidnapped a day earlier. He identified the victim as Carmelo Stella of a company called Moreno.