Mahmoud Othman, a Kurdish politician, blamed the attack on Ansar al-Sunnah, a Sunni Arab insurgent group, and Ansar al-Islam, a mostly Kurdish group with ties to al-Qaeda in Iraq.
Nonetheless, attacks in northern Iraq have increased in other mainly Kurdish towns in northern Iraq such as Kirkuk, as Sunni and Shia fighters flee a security crackdown in Baghdad.
Planning
Ahmed Nasruldin, an employee at a local university, was riding to work on a bus when the bomb detonated.
Your Views "The US has to withdraw completely from Iraq" Munzir Baig, Muscat, Oman Send us your views"The bus windows were smashed and my face and head were hurt by shrapnel. A woman beside me fell on my side, her shoulder was broken," he said.
"The US has to withdraw completely from Iraq"
Munzir Baig, Muscat, Oman
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Othman said authorities learned that fighters were planning a large attack a week ago when police arrested members of a cell in the town of Sulaimaniyah.
"During questioning they confessed that were getting training lessons in a neighbouring country and that was Iran," he said.
Kurdish political parties are allies in the Iraqi government of Nuri al-Maliki, the prime minister.
Jalal Talabani, the Iraqi president, is an ethnic Kurd.
Journalists killed
Also on Wednesday, four Iraqi journalists were killed as gunmen opened fire on their car near the northern city of Kirkuk.
The police said one of the journalists was the well-known director of a local media organisation which publishes several newspapers.
The attack took place southwest of Kirkuk near the small town of Rashad.
It was unclear if the shooting was random or because the four were journalists.
The Vienna-based International Press Institute said in April that 46 journalists were killed last year in Iraq, of whom 44 were Iraqis.
On Sunday, a Russian freelance photographer was killed in a roadside bomb attack north of Baghdad while on patrol with US forces.
Six soldiers were also killed in that attack.