The attack took place in Iraq's southeastern Maysan province in the district of Al-Majer al-Kabir.

The two security guards were "wounded in a Kalashnikov attack which targeted two cars belonging to Sinopec", the source said, speaking on condition of anonymity.

Chinese workers were also in the vehicles.

Sinopec has operated in the district since 2013.

Iraq has been left awash with weapons after decades of conflict, and the attackers have not been identified.

In December, a rocket and gunfire targeted the premises of Chinese oil services company ZPEC in the southern province of Nasiriyah, without causing any casualties or damage, officials said.

Chinese companies operate in oil fields across Iraq, and Beijing is the main market for Iraqi oil, taking some two fifths of the country's crude exports.

Iraq is the second-largest producer in the Organization of the Petroleum Exporting Countries, and oil accounts for more than 90 percent of its revenues.

In November, the country exported more than 98 million barrels of crude that brought in more than $7.6 billion, according to the oil ministry.

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SINOPEC - CHINA PETROLEUM & CHEMICAL CORPORATION