Gunmen in northern Nigeria attacked a university theater used for church services, killing at least 15 people.

Security officials say the gunmen threw small explosives into the site at Bayero University in Kano on Sunday, then fired on worshippers as they ran outside.

A faculty member at the university, Dr. Nasir Fagge, told VOA the killings happened at two locations at the school, and that security had been increased in the days leading up to the attack in light of other deadly incidents in the city.

He also said three professors were among those killed.

One of at least 22 people wounded in the Sunday's attack described the assault as coming just before service began.

“We were about to start the mass, then we start hearing gunshots, pah pah pah, and I ducked down because I am a retired soldier, and I said I will not run away to anywhere.”

Authorities said the attackers fled before security officers arrived, prompting police to cordon off the area, keeping out even emergency personnel for a time.

No one has claimed responsibility for the attack, which resembled others carried out by the Islamic militant group Boko Haram.

The group claimed responsibility for deadly attacks on Thursday at the offices of This Day newspaper in the northern city of Kaduna and the capital, Abuja.

Boko Haram, whose name means “Western education is a sin” in the Hausa language, is trying to turn Nigeria into an Islamic state. It has killed more than 1,000 people since 2009.

Nigerian President Goodluck Jonathan has been under increasing international pressure to bring an end to the violence.

Nigeria, Africa's most populous nation, is split between the majority-Muslim north and the predominantly Christian south.