KANO, Nigeria >> Gunmen attacked a Catholic Mass on a university campus Sunday in northern Nigeria, using small explosives to draw worshippers out before shooting those who fled, killing at least seven people, authorities said.

The attackers targeted an old section of Bayero University’s campus where religious groups use a theater to hold worship services, Kano state police spokesman Ibrahim Idris said. The assault left many others seriously wounded, Idris said.

“By the time we responded, they entered (their) motorcycles and disappeared into the neighborhood,” the commissioner said.

After the attack, police and soldiers cordoned off the campus as gunfire echoed in the surrounding streets. Abubakar Jibril, a spokesman for Nigeria’s National Emergency Management Agency, said security forces initially refused to allow rescuers to enter the campus. Soldiers also turned away journalists from the university.

Military spokesman Lt. Iweha Ikedichi said at least seven people had been killed in the attack. He declined to comment further.

No group immediately claimed responsibility. However, Idris said the attackers used small explosives packed inside of aluminum soda cans for the assault, a method previously used by a radical Islamist sect known as Boko Haram.

Boko Haram is waging a growing sectarian battle with Nigeria’s weak central government, using suicide car bombs and assault rifles in attacks across the country’s predominantly Muslim north and around its capital Abuja. Those killed have included Christians, Muslims and government officials. The sect has been blamed for killing more than 450 people this year alone, according to an Associated Press count.

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.

In January, a coordinated assault on government buildings and other sites in Kano by Boko Haram killed at least 185 people. In the time since, the sect has been blamed for attacking police stations and carrying out smaller assaults 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. Late Thursday night, gunmen also bombed a building at the campus of Gombe State University, though authorities said no one was injured in the attack.