The 159,000-dwt United Leadership (built 2005) is about five miles off Mohammedia in Morocco, according to information from IHS Maritime reported by Bloomberg news agency.

The ship, which is operated by Greece’s Marine Management Services and was sailing to the US Gulf, turned back on May 30 after getting about 190 miles west of Gibraltar.

Iraq’s oil marketing company Somo claims the oil shipment is illegal under the terms of the Iraqi constitution.

Nobody was immediately available at Marine Management Services to comment, but the company says executives are meeting and will revert later.

Bloomberg says the Kurdish news site Rudaw yesterday quoted a spokesman for the Kurdistan Regional Government claiming the tanker had “arrived at its destination”. But it did not specify what destination.

Claims that the oil shipment is illegal will discourage potential buyers for it, say energy analysts.

The dispute escalated last month when the Kurds began pumping oil through a pipeline to Ceyhan, the Turkish port in the Mediterranean where the United Leadership was loaded.

Iraq said on May 23 it had sought arbitration over Kurdish oil sales at the International Chamber of Commerce, but Somo has added that traders should not purchase the cargo.

The Kurdish region of Iraq is estimated to have reserves of about 45 billion barrels of crude oil compared with Iraq’s total of some 150 billion barrels.