A suicide bomber detonated an explosives-rigged vehicle in the heart of the usually secure Iraqi Kurdish regional capital Arbil on Wednesday, a spokesman said.
The bomber hit the main checkpoint on the way to the provincial government headquarters in the northern city just before noon (0900 GMT), provincial council spokesman Hamza Hamed said.
Hamed said there were casualties in the attack, but the number was not immediately clear.
The Wednesday bombing is the worst attack to hit Arbil since September 29, 2013, when militants struck the headquarters of the asayesh security forces in the city, killing seven people and wounding more than 60.
In that attack, the asayesh said a suicide bomber detonated explosives at the entrance to their headquarters, after which they killed four more would-be bombers before a fifth blew up an ambulance rigged with explosives.
Iraq's three-province autonomous Kurdish region is generally spared the rampant violence plaguing other parts of the country.
But its security forces are battling the Islamic State jihadist group, which spearheaded an offensive that has overrun large areas of Iraq since June, making it a more prominent target for militants.
There was no immediate claim of responsibility for the Wednesday Arbil attack.
But suicide bombings are usually carried out by Sunni extremists in Iraq, including a series of blasts claimed by IS in recent weeks.