"The United States strongly condemns the continued terrorist attacks in Iraq, including the suicide car bomb attacks today in Basrah and the Iraqi Kurdistan Region in front of the Arbil Provincial Council Building that took a number of innocent lives," the US State Department said in a statement.

"We extend our condolences to the families of the victims and hope for a rapid recovery for those who were injured," the US statement said.

"The Iraqi people are determined to stand against the violence and horrific ideology of the Islamic State of Iraq and the Levant (ISIL)," the US government said, using an alternate acronym for IS.

A bomber in an explosives-rigged vehicle hit the main checkpoint on the way to the provincial government headquarters in the northern city just before noon.

Two of the four killed were police, said officials who put the number of injured at 29.

The blast shattered car windows, scarred vehicles with shrapnel and left glass and debris scattered across the blood-stained street.

Iraq's three-province autonomous Kurdish region is generally spared the rampant violence plaguing other parts of the country.

Officials said the bombing is the worst attack on Arbil since September 29, 2013, when militants struck security force headquarters, killing seven people and wounding more than 60.