The Iraqi government is seeking to restore calm in the southern province of Basra, the country's main oil production center, after hundreds of foreign oilmen were hastily evacuated amid violent protests by Iraqi oil workers.

The evacuation, after rioters wrecked a camp used by Houston-based Schlumberger Inc., the world's largest oilfield services company, came amid a worsening surge of sectarian warfare across Iraq that threatens to undermine a drive by the government to boost oil production to record levels and challenge Saudi Arabia as the world's leading oil power.

Until recently, the bloodletting, largely the work of Sunni extremists of al-Qaida against Iraq's Shiite majority, had not seriously threatened the Basra oil fields, which produce around two-thirds of Iraq's output.

But in the last few weeks the Shiites around Basra, Iraq's second largest city, have become targets, and any major escalation could impact heavily on Iraqi oil production, the country's economic mainstay.

There was trouble with Shiite oil workers at the giant Rumaila field, Iraq's biggest and the core of Baghdad's oil expansion program, during Ashura, a highly emotive 10-day period of mourning by Shiite Muslims for the Prophet Mohammed's grandson, the widely revered Imam Hussein killed in 680 A.D.

It started Monday at the Schlumberger camp near Rumaila when Shiite oil workers refused the orders of a British security official to take down posters of Imam Hussein.

The official then ripped them down himself. He was attacked by workers and reportedly drew a pistol, fired several shots and wounded at least one Iraqi.

Schlumberger suspended operations, called in two private airliners Thursday and flew out 300 employees and dependents. Several hundred other foreigners left Basra on scheduled flights.

Iraqi authorities moved swiftly to contain the trouble. The state-run Southern Oil Co. said Rumaila was not affected.

Thamor Ghadhban, chairman of the advisory commission to Iraq's Council of Ministers, downplayed the trouble and said Schlumberger would resume operations next week.

That may be the end of that episode. But the violence reflected the unease pervading the country as sectarian bloodshed escalates, with scores of people killed or wounded every day amid a Sunni-Shiite conflict that's spreading across the Arab world, centered on Iraq and Syria.

Iraq's oil industry in the north centered on the Kirkuk oilfields, which sits on a third of the country's stated oil reserves of 150 billion barrels, has been under constant attack for months.

Gunmen attacked the Ahdeb oil field in eastern Wasit province Nov. 1. The following day, a major pipeline running to Turkey's Ceyhan terminal on the eastern Mediterranean through Nineveh province was shut down after it was bombed.

The violence, which consists largely of suicide and car bombings by al-Qaida and its allies against Shiites, has reached the bloodiest levels since 2008, with more than 7,000 people killed so far this year.

That doesn't compare with 2006, the deadliest year following the 2003 U.S. invasion with 29,287 violent deaths.

But this year is different because the flames of these sectarian hatreds are being fanned by the worsening civil war in neighboring Syria.

The Sunni extremists of al-Qaida are also fighting in Syria against the Damascus regime, but increasingly Iraqi Shiites, trained by Iran and Lebanon's Hezbollah, are joining the conflict and fighting the Sunnis.

This is reflected in the growing number of public funerals of Shiite fighters killed in Syria that are being held around Basra in recent weeks.

The fallout from Syria could escalate the bloodshed in the Shiite-dominated provinces of Basra and Dhi Qar as well, with Shiite gunmen retaliating against Sunnis for al-Qaida's depredations.

That could well spill over into Basra province and possibly impede oil production in the megafields that Baghdad's counting on to bolster its production levels from the current level of slightly more than 3 million barrels per day to 4 million bpd by 2014 and 9 million bpd by 2020.

Rumaila, operated by BP with China National Petroleum Co., holds an estimated 17 billion barrels and currently produces around 1.4 million barrels per day. That's one-third of Iraq's current output.

The consequences of giant southern fields like Rumaila, Zubair and West Qurna, the ones that will make Iraq another Saudi Arabia, having to scale back production, or even shut down, could be catastrophic for Baghdad.