KANO, Nigeria — A police commissioner says at least six people were killed in an attack on a university campus in northern Nigeria where Catholics were holding a worship service.

Kano state police commissioner Ibrahim Idris says the attack happened Sunday morning on an old section of Bayero University's campus.

Idris says the gunmen rode into the campus on motorcycles and used small explosives within soda cans to scare worshippers out of the church. Idris says the gunmen shot those who fled.

Idris says there are "many seriously injured."

No group immediately claimed responsibility for the attack, though it mirrors tactics previously used by a radical Islamist sect known as Boko Haram. That group carried out a coordinated assault in Kano in January that killed at least 185 people.

Witnesses said the attack hit an old section of the campus of Bayero University. Abubakar Jibril, a spokesman for Nigeria's National Emergency Management Agency, said at least three explosions struck on and around the campus, and that sporadic gunfire was still ongoing Sunday morning.

A police spokesman referred calls for comment to Nigeria's military. Military spokesman Lt. Iweha Ikedichi said soldiers and police had surrounded the university and were searching for the gunmen who carried out the attack.

"There were casualties, but I don't have exact figures," Ikedichi said. "Some are so injured and have been rushed to local hospitals."

No group immediately claimed responsibility. The attack Sunday comes as Nigeria faces a growing sectarian battle between its weak central government and a radical Islamist sect known as Boko Haram.

Diplomats and military officials say Boko Haram has links with two other al-Qaida-aligned terrorist groups in Africa. Members of the sect also reportedly have been spotted in northern Mali which Tuareg rebels and hardline Islamists seized control of over the past month.

The sect has been blamed for killing more than 450 people this year alone, according to an Associated Press count.

In January, a coordinated assault on government buildings and other sites in Kano by the sect killed at least 185 people. In the time since, the sect has been blamed for attacking police stations and carrying out smaller attacks in the city.

On Thursday, the sect carried out a suicide car bombing at the Abuja offices of the influential newspaper ThisDay and a bombing at an office building it shared with other publications in the city of Kaduna. At least seven people were killed in those attacks.