The attacks came just after the results of the region’s parliamentary elections were announced, but much of the speculation surrounding the motivation for the attack centered on Syria, where Kurdish militias, some of them supported and trained by the security forces in Iraqi Kurdistan, have been fighting against jihadist groups linked to Al Qaeda. No group immediately claimed responsibility for the bombings.

“We all know that Kurdistan is part of an unstable region, and security breaches sometimes happen even in developed countries, and I think that what is happening in Syria has something to do with today’s explosions,” said Shwan Taha, a Kurdish member of Iraq’s Parliament in Baghdad.

In a statement, the United Nations office in Baghdad expressed shock at the “daring attack.”

“For many years, the city of Erbil has benefited from peace and security, and I urge the regional and national authorities to work together to ensure that calm and tranquillity will continue to prevail and that those responsible for the attack are brought to justice,” Nikolay Mladenov, the United Nations representative to Iraq, said in the statement.

The self-governing Iraqi Kurdish region has been a haven of relative security and prosperity compared with the rest of the country, and it has attracted substantial foreign investment, including from foreign oil companies eager to develop the region’s vast oil reserves. During the years that American troops were fighting in Iraq, not a single American soldier was killed in combat in Iraqi Kurdistan. But the attacks on Sunday demonstrated that no place in Iraq was truly safe, as the war in Syria increasingly spills over its borders and as Iraq’s own Sunni insurgent groups accelerate their attacks.

Iraq’s Qaeda affiliate has gained strength across the country, but particularly in the northern city of Mosul, not far from the border with Iraqi Kurdistan, leading to speculation that groups there could have been behind the bombings.