Attackers in northern Nigeria tossed homemade bombs during a Christian service Sunday and then opened fire as panicked worshippers tried to flee, killing at least 15 people.

Security officials say the gunmen were riding motorcycles when they launched an assault at Bayero University in Kano.

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

At least 22 people were wounded.

No one has claimed responsibility for the massacre, which is similar to other attacks 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.