The Nigerian military has taken control of a VLCC detained for three months in Equatorial Guinea and taken it back to sea for further investigations into an oil dispute, according to the ship’s representatives.

Ship tracking services showed the 300,000-dwt Heroic Idun (built 2020) heading away from the island of Bioko. It is accompanied by two tugs and a Nigerian military gunboat, according to maritime lawyer James Gosling, representing the tanker owner, Ray Car Carriers.

Lawyers for the ship and 26-strong crew say the move is unlawful and had gone to Nigeria’s courts and lobbied the International Maritime Organization in an unsuccessful attempt to prevent the ship from leaving Equatorial Guinea.

The tanker is being taken to the Bonny Offshore terminal at Port Harcourt, Nigeria, and the crew was forced to sail under “extreme and armed duress”, said Gosling.

It was not immediately clear if all 26 crew members were on the tanker or some were on accompanying vessels.

The Nigerian navy said the tanker was being brought back to Nigeria “in order to clear any misconceptions about its involvement in crude oil theft”.

The departure from Bioko is the latest episode of a saga that has seen the ship and crew suspected of “economic espionage” after leaving the Akpo oil terminal at Bonny on August 8 when crew mistakenly identified a Nigerian naval vessel as a potential pirate ship.

The Heroic Idun was later arrested by an Equatorial Guinea vessel and taken to Bioko where lawyers for the owners and operators have tried to get it freed for weeks. Local authorities failed to free the ship as promised after a fine of $2m was paid, said lawyers.

The International Tribunal for the Law of the Sea confirmed on Thursday that it had received an application from the Heroic Idun’s flag state, the Marshall Islands, for its release from Equatorial Guinea. But the ship has left before any hearings into the case.

The ship’s representatives said on Thursday that the manufacturer had disabled power to the engine to try to prevent it from moving. But the engine was restarted because of concerns that the tugs were not suitable to tow the vessel and is now moving under its own power.

The Nigerian navy said that the Heroic Idun could be charged with unauthorised entry of a restricted zone around an oilfield, illegally attempting to load crude and falsely accusing a Nigerian navy ship of piracy.

“If the vessel is found innocent, it will be released. If found guilty of breaking the laws of Nigeria, the appropriate sanctions will be enforced, to send a strong message of deterrence,” said the navy on Wednesday.

The owners and operators have said the master had acted properly and the master had issued a note of readiness before leaving the terminal.

“The treatment received by the crew shows a blatant disregard for basic human rights and international law,” said Rolf Thore Roppestad, the CEO of Gard, the ship’s P&I insurer.

Rolf Thore Roppestad, the chief executive officer of Gard, has condemned the detention of the Heroic Idun Photo: Gard

Presidential elections are due to be held early next year in Nigeria. The government under President Muhammadu Buhari has come under pressure to tackle rampant corruption with the authorities claiming more than $3bn has been lost to crude oil theft since last year.