Kano - Motorcycle-riding gunmen have killed a police officer guarding a state official's house in northern Nigeria, police said on Thursday, with a wave of such shootings blamed on an Islamist sect.

The shooting on Wednesday night occurred in the city of Bauchi, where suspected Islamists from the Boko Haram sect attacked a prison last month and freed more than 700 inmates.

"There was an attack on the residence of the commissioner for special duties, where a police security attached to the house was killed," state police commissioner Danlami Yar'Adua said.

"The gunmen arrived on a motorbike and opened fire outside the house, killing the policeman, and sped away."

He declined to say whether Boko Haram members were suspected in the attack outside the home of Musa Muazu Badara, adding the investigation was ongoing.

A commissioner is the equivalent of a minister on the state level in Nigeria. Special duties commissioners handle a variety of tasks at the governor's discretion.

One witness who said he was at the mosque next to the house, Halilu Dauda, said by phone that he heard four gunshots and saw two officers on the ground when he went outside.

A wave of such killings and other attacks in Nigeria's north in recent months have raised alarm over the sect, which launched an uprising last year crushed by a brutal assault that left hundreds dead.

Troops were deployed in the northern Nigerian city of Maiduguri this week after a series of attacks blamed on Boko Haram. On Monday, suspected sect members attacked and torched a police station in the city.