The policemen was at work when unknown gunmen entered the family's home and fired a single shot into each of the victims, said Colonel Sherzad Mofri, who listed the children's ages as three, six and nine.

"They killed his wife and three children who were sleeping beside their mother," said Mofri, announcing that an investigation was under way.

The attack happened in the city's Banjar neighbourhood, an area where Kurds deported by Saddam Hussein returned and built homes following the dictator's overthrow in the US-led invasion of 2003.

Kirkuk has a mixed population of Arabs, Kurds and Turkmen, and longstanding Kurdish demands for the city to be incorporated in their autonomous region in the north have fanned ethnic tensions.