Lawyers representing the 26-strong crew of a tanker at the centre of an oil theft probe have launched legal action to stop them being taken to Nigeria in “flagrant violation” of their rights after nearly three months of detention.

The 300,000-dwt VLCC Heroic Idun (built 2020) was stopped in international waters at the request of Nigeria and has remained since 13 August off the island of Bioko, in Equatorial Guinea.

The ship came under investigation after the tanker left Nigeria’s Akpo terminal where it had been due to load an oil cargo because the master feared an attack from pirates following an approach in the darkness by an unidentified ship.

The crew later discovered the unidentified ship was a Nigerian navy vessel. The Heroic Idun was subsequently stopped by an Equatorial Guinea naval ship and escorted to Bioko while Nigeria has sought to bring back the ship for further investigation.

Lawyers for the Ray Car Carriers-owned Heroic Idun say any transfer would amount to an unlawful rendition and has sought to declare the move as unlawful in the Nigerian courts. Stephen Askins, a lawyer representing the owners, said in a LinkedIn post that the application was an “extraordinary development and a first in Nigeria”.

The Marshall Islands, its flag state, is also understood to be preparing a claim to the International Tribunal for the Law of the Sea to try to free the vessel and its crew of 16 Indians, eight Sri Lankans, a Filipino and the Polish chief engineer.

“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.

“We are deeply concerned with the latest developments and will continue to do everything we can to ensure the crew is safe.”

The men have been denied access to lawyers or consular officials, according to supporters, with many of the “mentally shattered” crew having caught tropical diseases such as malaria and typhoid.

The Polish chief engineer was taken from hospital this week to prepare it for sailing to Nigeria along with other crew members who had been taken from the ship. He was threatened with being taken by aircraft to Nigeria if he refused, according to Askins.

The Marshall Islands countered the efforts to move the ship with formal detention order banning the vessel from sailing because of the state of the crew. It led to 15 crew members being taken off the ship again to a small, unfurnished room, according to the ship’s representatives.

The shipowner paid a fine close to $2m in early October for failing to fly the flag of Equatorial Guinea in its water but the promised release of the vessel and crew never happened, said the ship’s war risks insurer DNK.

“It is close to unbelievable to see how seafarers are still criminalised and detained for months on end apparently without due process in certain parts of the world, now in Equatorial Guinea,” said its CEO Svein Ringbakken.

DNK CEO Svein Ringbakken. Photo: Bob Rust

The investigation into the Heroic Idun comes before the EU begins an embargo on seaborne Russian crude oil imports from December because of its invasion of Russia.

Analysts said that Europe will be looking for more barrels from West Africa to counter the loss of Russian imports.

“By acting like this, they are shooting themselves in the foot,” said Ringbakken. “There is no due process for the crew or ship and it is making that area of the world even more difficult.”