Kano - Gunshots and explosions rang out on Wednesday in Nigeria's biggest northern city Kano, as the military exchanged fire with suspected militants from the Boko Haram Islamist sect.

Clashes between Boko Haram gunmen and security forces have flared up several times in Kano since the sect killed 186 people in Nigeria's second largest city last month, its deadliest attack so far.

“There was a shootout and four arrests were made while the early morning operation lasted,” local spokesperson for the Joint Military Taskforce (JTF) Ikedi Iweha Ikidichi said, declining to take further questions.

Boko Haram, which is waging an insurgency to try to impose sharia law across Africa's most populous nation split evenly between Muslims and Christians, has become increasingly sophisticated and deadly in its methods in the last six months.

It often sets off multiple bombs in succession or follows them up with shooting sprees.

It claimed responsibility on Tuesday for attacks in its home base in the northeast town of Maiduguri this week which killed at least 8 people.

“We were stopped from coming out for our early morning prayers, we couldn't leave the house. At about 5am the gunshots and explosions started,” Stephen Ahmed, a Kano resident, told Reuters by phone.

A spokesperson for the National Emergency Management Agency said there were as yet no recorded casualties from the fighting, noting that it mostly happened in the early hours, when a curfew was still in force in Kano.

Although the majority of the sect's attacks still occur in its home base in the northeast, its threat has spread and it has become more ambitious.

A week ago, gunmen suspected to be from Boko Haram stormed a prison in Kogi state in central Nigeria, killing one warden and freeing 119 prisoners, the prison authorities said.

A bomb exploded near a church in the Nigerian town of Suleja, on the edge of the capital, on Sunday, wounding five people.

On Christmas Day, a bomb blast claimed by Boko Haram against a Catholic Church in Madala, just outside Abuja, killed 37 people and wounded 57.

Nigeria's security forces are struggling to contain Boko Haram and a series of bloody crackdowns have often served to radicalise the local population against them. - Reuters