Gunmen on a bicycle have shot dead a guard outside of a church in northeastern Nigeria, police said on Monday, amid a wave of attacks blamed on Islamist group Boko Haram.

The attackers arrived on a bicycle outside the church in the city of Potiskum on Sunday, police said.

Many previous such attacks have been carried out by gunmen on motorcycles, but motorbikes have been banned in the city as a security measure.

"We received the news of an attack on the First Baptist Church in Potiskum yesterday afternoon," state police commissioner Lawan Tanko said.

"Two gunmen riding a bicycle pretended to be passers-by and shot dead the church guard and disappeared through back streets. No arrests have been made yet."

Residents said the guard was a retired police officer, but Tanko could not confirm the information.

Boko Haram has been blamed for scores of attacks in Nigeria's north. Its deadliest raid yet occurred on January 20 in Kano, Nigeria's second-largest city, when coordinated bombings and shootings left at least 185 people dead.