The assault late on Thursday evening in the southern city of Basra came after the attackers had threatened to sabotage Iraq's crucial oil infrastructure to protest the ongoing clashes pitting armed fighters against US and Iraqi forces in Najaf.
The fighters held drilling equipment and other gear, to the ground. The fire then spread to the company's offices.
No change in exports
Meanwhile, an oil official at the company said Iraq's oil exports are still flowing at one million barrels per day through southern terminals despite the attack.
Exports have been running at one million bpd, or half of normal, since saboteurs attacked one of two pipelines feeding the offshore terminals on 9 August.