Gunmen attacked worship services at a university campus 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 deadlier attack targeted an old section of Bayero University’s campus in the city of Kano where churches hold Sunday services, with gunmen killing at least 16 people and wounding at least 22 others, according to the Nigerian Red Cross.

A later attack in the northeast city of Maiduguri saw 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 worshippers ran out in an attempt to escape, only to be shot by the waiting gunmen, the commissioner 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 refused to allow rescuers to enter the campus. Soldiers also turned away journalists from the university.

The city of Maiduguri, the target of second attack, is where Boko Haram once had its main mosque.