One resident said he saw many casualties in the street and several buildings had collapsed.


Kirkuk is just outside the borders of the largely autonomous Kurdistan region and its population is a volatile mix of Kurds, Turkmen and Sunni and Shia Arabs.


Iraqi security forces are frequently targeted by bombers seeking to undermine the US-backed Iraqi government.


Police in many areas of Kirkuk have also been infiltrated by militias, making them a target for rival armed groups.