A minimum of 102 people were killed by at least two car bombs that exploded outside a Nigerian mosque in Kano Friday, a hospital worker who counted the bodies told the Associated Press. Gunfire was heard after the bombs detonated  outside the mosque as congregants were preparing to pray, Al Jazeera reported.

A mortuary worker at the Murtala specialist hospital told AP, “I was asked to be counting those deposited, and I counted over 102 dead bodies before I was asked to stop.”

Although nobody has taken responsibility for the bombing, it is believed to be the work of Boko Haram, the extremist Islamist group that for five years has waged a campaign for a separate state in the northern Nigeria ruled by Islamic law. 

It is thought the group was retaliating against the church’s emir, Sanusi Lamido Sanusi, who had called for Nigerians to fight Boko Haram. “[W]hen they attack towns, they kill boys and enslave girls ... People must stand resolute," Sanusi recently told the Daily Post in Nigeria. “People should be sensitized on the importance of being on the alert. And they should prepare, they should acquire what they will defend themselves with.”

A representative of United Nations Secretary-General Ban Ki-moon pledged the U.N. would support Nigeria in its fight against terrorism, calling the attack “horrific,” AP said. And Nigerian President Goodluck Jonathan said his government was determined to “continue to take every step to put an end to the reprehensible acts of all groups and persons involved in acts of terrorism.”

The bombing of the mosque came one day after a bomb at a bus station in Adamawa killed five policeman and 35 civilians. According to Amnesty International, more than 1,500 have been killed because of the insurgency in Nigeria this year.