KANO, Nigeria - Gunmen attacked worship services at a university and a church Sunday in northern Nigeria, killing at least 21 people in coordinated assaults that saw panicked Christians gunned down as they tried to flee, witnesses and officials said.

The first attack targeted a section of Bayero University's campus in Kano where churches hold services, with gunmen killing at least 16 people and wounding at least 22, according to the Nigerian Red Cross.

In a later attack, in the northeast city of Maiduguri, gunmen open fire at a Church of Christ in Nigeria chapel, killing five people, including a pastor preparing for Communion, witnesses said.

No group immediately claimed responsibility, but the attacks bore similarities to others carried by a radical Islamist sect known as Boko Haram.

The Bayero University attack occurred around an old theater and lecture halls where local churches hold services, Kano state police commissioner Ibrahim Idris said. The gunmen rode into the campus on motorcycles, then threw small explosives made out of soda cans around the area, Idris said.

The worshipers ran out in an attempt to escape, only to be shot by the waiting gunmen, the commissioner said.

"By the time we responded, they . . . disappeared into the neighborhood," he 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 refused to allow rescuers to enter the campus. Soldiers also turned away journalists from the university.

The city of Maiduguri, the target of a second attack, is where Boko Haram once had its main mosque. Representatives of the group, who typically speak to journalists in telephone conference calls, could not immediately be reached Sunday.