By Isabel Coles
ARBIL, Iraq (Reuters) - Militants launched a coordinated suicide and car bomb attack on the headquarters of the security services in the capital of Iraq's usually peaceful Kurdistan region on Sunday, killing six people in the first major assault there since 2007.
Kurdistan has largely managed to insulate itself from the violent instability that afflicts the rest of Iraq, where insurgent groups including the Sunni Islamist al Qaeda have been regaining momentum this year and striking on a near daily basis.
The relative security has attracted some of the world's largest oil companies including ExxonMobil and Chevron Corp to the region, which is autonomous and polices its own borders. Most oil firms operating in Kurdistan are headquartered in Arbil.
Security forces said the attack began early on Sunday afternoon when they opened fire on a minivan that tried to enter their compound on Sixty Metre road in the capital Arbil without authorization. The driver detonated his vehicle at the entrance.
Four suicide bombers armed with guns and grenades then tried to force their way inside but were shot down, the Iraqi Kurdish security forces added in a statement.
An ambulance also exploded at the scene. The statement said it was driven by a militant but another security source said the blast was caused by a car blowing up nearby.
Six militants and six members of the security forces were killed and at least 42 others wounded, the authorities said. Security across the city was tight after the attack.
No group immediately claimed responsibility for the explosions, which occurred a day after results of the region's parliamentary elections were announced.
"This shows that those who resent Kurdistan do not want it to be victorious," read the security forces' statement. "These kind of attacks will make us more determined to confront the terrorists," it added.
The statement said security forces had thwarted many attacks since 2007, when a truck full of explosives blew up outside the interior ministry, not far from the site of Sunday's bombings.
The United Nations' new envoy to Iraq Nicolay Mladenov said he was shocked.
"For many years, the city of Arbil has benefited from peace and security and I urge the regional and national authorities to work together to ensure that calm and tranquility will continue to prevail."
The civil war in neighboring Syria has brought sectarian and ethnic tensions in Iraq and the wider Middle East to a boil.
In recent months, a Syrian Kurdish militia has been battling mainly Arab rebels and Islamist fighters, as the focus of the conflict changes from removing President Bashar al-Assad into a struggle for control over territory and resources.
Yahya Kubaisi, an analyst at Iraq's Institute for Strategic Studies, said Islamist militants might have carried out the attack in Arbil in revenge for the Kurdistan Regional Government's perceived support of Kurds fighting them in Syria.
(Additional reporting by Ahmed Rasheed in Baghdad; Editing by Andrew Heavens)