Witnesses in northern Nigeria say attackers tossed homemade bombs at worshippers during a Christian service and then opened fired as they 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, where the service was taking place on Sunday.

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

Witnesses report many people were wounded, although it was unclear how many.

There was no immediate claim of responsibility for the massacre, which follows similar attacks claimed by the Islamic militant group Boko Haram.

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

The group is believed to be responsible for more than 1,000 deaths since 2009.

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

The group claims it is fighting to impose strict Islamic law and does not recognize country's constitution.

Nigeria – Africa's most populous nation – is divided roughly in half between the majority-Muslim north and the predominantly Christian south.