A police officer walks past a burnt out shopping mall in Maiduguri, Nigeria.

Kano, Nigeria - Gunmen have killed at least four policemen in the last two days in attacks in the northern Nigerian city of Kano, which has been repeatedly hit by violence blamed on Islamists, authorities said.

The latest attack occurred Tuesday morning when gunmen opened fire on a police patrol in Kano, the largest city in the country's mainly Muslim north.

“Two policemen lost their lives when some gunmen in a vehicle opened fire on their patrol van around 8:00 am today at Yanawaki area,” police spokesman Magaji Majia told AFP.

He said another policeman was seriously injured in the attack, the latest in the city where Islamist extremist group Boko Haram has been active. Majia said no arrests were made as the gunmen fled after the attack.

The attack came after a similar incident on Monday, when gunmen killed two policemen and injured two civilians at a police checkpoint in another area of Kano, according to a military spokesman.

Violence related to Boko Haram's insurgency has left some 3 000 people dead since 2009 in Nigeria, including killings by the security forces.

The group's deadliest ever attack was in Kano in January 2012, when some 185 people were killed in coordinated gun and bomb attacks.

Criminal gangs and imitators however also carry out violence under the guise of the group. - Sapa-AFP