The killing of Abdul Sattar Taher Sharif, 74, who held a New Zealand passport, came 10 days after he wrote an article in the Kurdish-language monthly Lizin criticising Kurdish leaders for not pushing harder for the city's incorporation into the autonomous Kurdish region.

Sharif was shot dead by unknown gunmen at midday (0900 GMT) on a road just north of Kirkuk, assistant police chief Major General Torhan Yussef told AFP.

Kirkuk University assistant president Mohammed al-Naimi described the murder of the psychology professor as "a big loss to Iraq."

Under the Iraqi constitution, a referendum had due to be held by last year on longstanding Kurdish claims for Kirkuk and its oil wealth to be incorporated in their autonomous region in the north.

But in December, Kurdish leaders agreed to a six-month postponement of the vote at the recommendation of the United Nations.

Kirkuk has been gripped by ethnic tension since the US-led invasion of 2003, with Arab and Turkmen residents fearful they would be marginalised if the city were handed over to the Kurds.

Under Saddam Hussein's regime, the city was the scene of massive population upheaval with tens of thousands of Kurdish residents being expelled to make way for Arab settlers.