Gunmen bombed a police station on Sunday outside Nigeria's second city Kano, the police and witnesses said, leading to an hour of gunbattles in a region plagued by attacks from Islamist sect Boko Haram.

Kano state and its capital city of 10 million people have been under siege by gunmen from Boko Haram, which wants to impose sharia law across Nigeria.

We were able to push them out of the area but they burnt part of the police station, Kano police commissioner Ibrahim Idris said. It was a blast that caused damage to the station.

Boko Haram's attacks have become more sophisticated and deadly in Africa's top oil producer. A series of gun and bomb attacks, mostly on police stations, killed 186 people in Kano on January 20.

Witnesses said gunmen and armed police were in a shoot out for around an hour after the explosion at the police station at Naibawa district outside Kano.

We are scared. The police and Boko Haram members are battling each other and there is gunfire everywhere, Usman Ibrahim Bello, a local resident told Reuters.

In an audio tape posted on the Internet on Thursday, the purported leader of Boko Haram, Abubakar Shekau, threatened to kill more security personnel and kidnap their families, and accused U.S. President Barack Obama of waging war on Islam.

Boko Haram, a movement loosely modelled on the Afghan Taliban whose name translates as Western education is sinful, has been behind almost daily killings in its home base in the largely Muslim northeast. Its violence has spread west into other parts of the north and the capital Abuja since last year.

(Reporting by Mike Oboh; Writing by Joe Brock)