NOC’s chief of operations, Saad al-Karbalaie, was killed in the northern oil city of Kirkuk after gunmen forced him to stop his vehicle as he was leaving his office and then shot him, police sources said.

There was no immediate claim of responsibility for the attack on Karbalaie, who was supervising production and export facilities in Kirkuk.

Major oil producer and OPEC member Iraq faces security challenges from the ultra-hardline Sunni Islamic State of Iraq and Syria (ISIS) which controls a third of the country, and a sectarian conflict exacerbated by the group’s presence.

Baiji refinery, north of Baghdad, is a focal point for government efforts to slow the advance of ISIS. The complex has changed hands several times in months of fighting.