The autonomous region's security council said its counterterrorism unit had arrested Mazloum Dag, a 27-year-old from Turkey's Diyarbakir region.

The council had put out a wanted notice for Dag a day earlier in connection to Wednesday's killing of Turkish Vice Consul Osman Kose and two Iraqi nationals in the regional capital Arbil.

Turkey's Anadolu state news agency said the suspect is the brother of Dersim Dag, a member of Turkey's main pro-Kurdish party, the People's Democratic Party (HDP).

The HDP, the country's second largest opposition group, is regularly accused by President Recep Tayyip Erdogan of links to Turkey's outlawed separatist Kurdistan Workers' Party (PKK).

It "strongly" condemned the Arbil attack, calling it an "absolutely unacceptable provocation attempt".

The HDP also slammed the accusation that one of its deputies was "designated as a target because of his brother", without mentioning any names.

No group has claimed responsibility for the attack, but Ankara on Thursday launched a "comprehensive air operation" against the PKK in Iraqi Kurdistan's Qandil mountain area.

Since May, Turkey has been conducting a ground offensive and bombing campaign against Qandil to root out the PKK, considered a "terror organisation" by Ankara for its three-decade insurgency against the Turkish state.

Other air strikes Thursday night targeted "PKK bases and members" in the Makhmur area south of Iraq's northern city of Mosul, wounding two in a displacement camp, local sources told AFP.

The attack on Wednesday saw at least one gunman with two pistols fire on a group of diplomats in a restaurant in Arbil.

Kose and one Iraqi died Wednesday, while the second Iraqi succumbed to his wounds overnight.