The United Nations (UN) top envoy in Iraq strongly condemned the killing of a Turkish diplomat in an armed attack in Iraq's northern city of Erbil, urging for a thorough probe into the attack, Trend reports citing Xinhua.

Jeanine Hennis-Plasschaert, special representative of the UN Secretary-General for Iraq, said "this heinous attack cannot be justified under any circumstance and must be soundly condemned," according to a statement by the UN Assistance Mission for Iraq (UNAMI).

"I urge for maximum restraint and intensified efforts by the authorities to conduct a thorough investigation, apprehend the culprits and bring them to justice," the statement quoted the UNAMI chief as saying.

Earlier in the day, a Turkish consulate employee and a civilian were killed while another person was wounded when gunmen opened fire at a restaurant in the northern city of Erbil.

A local security source told Xinhua that security forces have cordoned off the area, intensified security measures at the city's entrances and launched a search campaign looking for the attackers who fled the scene immediately.