(Bloomberg) -- An oil supertanker that Nigeria tried to seize has been stuck off the coast of nearby Equatorial Guinea for more than 10 days, where it was impounded by local authorities.

The Nigerian navy said that its counterparts in Equatorial Guinea arrested the Heroic Idun on Aug. 12, four days after the same vessel allegedly tried to load a cargo of crude unlawfully from the deep-water Akpo field operated by TotalEnergies SE. The ship lacked the necessary clearance and left Nigerian waters before being intercepted by the Equatoguinean military, the navy said on Aug. 19.

The Nigerian navy said that the ship was on hire to trading giant Trafigura Group, but that appears to not be the case, according to a person familiar with the matter. The tanker was on lease to BP Plc from Mercuria Group at around the time the navy tried to seize it on April 8, according to another person with knowledge of the situation.

For its part, Europe’s biggest oil company said it hired the Heroic Idun to collect an Akpo cargo ten days after the Nigerian navy interrogated the ship but booked another carrier after the Idun was “unable to perform the lifting.” 

One potential explanation for the controversy is that the ship didn’t have the right paperwork at the time it arrived.

Loading programs show the cargo belonged to Prime Oil & Gas Cooperatief UA, which owns a 16% interest in the Total-operated license that contains the Akpo field. Prime declined to comment. Total “is not involved,” a spokesman said by email. “At no time was crude volumes transferred” to the vessel, the company said.

Equatorial Guinea is conducting its own investigation and Nigeria has started diplomatic procedures to take control of the tanker, which is currently anchored off the coast of Luba, the Nigerian navy said.

Nigerian authorities are under pressure to stem rampant crude theft from the country’s onshore pipelines. It would be highly unusual for such activity to occur in deepwater permits 200 kilometers off the coast.

Norway’s Hunter Group ASA announced the sale of the Heroic Idun last month but didn’t respond to an email asking who bought the tanker.

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