Shootings as a means of settling scores are far from rare in Iraq -- its legacy of war and sectarian conflict mean the country's 40 million people count some 7.6 million firearms, according to figures from the Small Arms Survey.

A Soran University engineering professor was shot dead in his home in the early hours, and the dean of the Salaheddin University law faculty, Kawan Ismail, was killed on campus shortly afterwards, provincial governor Omed Khoshnaw told reporters.

Police believe the shooter did not originally intend to kill the engineering professor, but rather his wife, who is a law professor at the same university and was away from home at the time, Khosnaw said.

The suspect was expelled from Soran University by the first victim's wife and was then refused a place at Salaheddin University by the second victim, the governor said.

He had been arrested several times previously after making death threats against the second victim, whose bodyguard was also wounded in the attack.