DUBAI - Major oil exporter Kuwait is dealing with another crude oil spill off its southern coast, state news agency KUNA said on Monday, the latest in a series of unexplained leaks in the Gulf Arab state in recent months.

KUNA said the latest spill has been detected in the Ras al-Zour area, where Kuwait National Petroleum Company (KNPC) is building the Middle East's largest oil refinery with a capacity of 615,000 barrels per day at a cost of $11.5 billion in contracts.

Kuwait's Environment Public Authority is monitoring the spill and is working with Kuwait Oil Company and marine authorities to control it, KUNA said, adding the size of the leak was still being assessed.

OPEC member Kuwait reported a leak in the same area last month. That was followed by another spill at Abu Fatira, about 15 miles (25 km) south of the capital Kuwait City, spanning one nautical mile.

There was also a limited spill from a pipeline at Kuwait's northern al-Ratqa field in July.

Kuwait's oil minister said last month that neighbouring Saudi Arabia and Iran had said they had not detected any oil spillage in their waters from the marine leaks.

(Reporting by Sylvia Westall; editing by Sami Aboudi, Greg Mahlich) ((sylvia.westall@thomsonreuters.com; Dubai Newsroom +971 56 216 6204; Reuters Messaging: sylvia.westall.thomsonreuters.com@reuters.net))