Security in the northern Iraqi oil fields is not a concern for British energy company Gulf Keystone Petroleum, its chief executive officer said.

"Security right now is not a concern for us," CEO John Gerstenlauer said in an operational update. "Everything is going along quite smoothly."

Iraqi Prime Minister Haider al-Abadi gave his approval during the weekend for a military assault on the western Iraqi city of Ramadi after the Sunni-dominated region was overrun by the group calling itself the Islamic State.

"The loss of Ramadi does not mean the tide of the campaign has turned, and we have long said that there would be ebbs and flows on the battlefield," U.S. Defense Department spokeswoman Elissa Smith said.

The Islamic group at various times held key Iraqi oil installations in its push out of the borders of the Syrian conflict. Several oil companies working in northern Iraq pulled staff out of the region as a security precaution as the conflict escalated late last year.

Gerstenlauer suggested low oil prices were more of an operational threat in the Kurdish north of Iraq than terrorism. The company is targeting about 36,000 barrels of oil per day. From mid-February to mid-March, the CEO said production was at zero because of the low price of oil.

The company, which has headquarters in London, is producing oil from nine wells in the Shaikan development in the Kurdish north of Iraq. Total production was around 40,000 barrels of oil per day at the end of 2014.