Pirates in Togo have released a tanker with 24 Russian crew on board after siphoning off part of the gas oil cargo, a spokesman for the ship's Greek company said on Thursday.

"The ship has been released and the crew are safe," said the representative on behalf of Athens-based Golden Energy Management.

"It is now en route to a safe destination," he added.

The pirates hijacked the Energy Centurion on Tuesday after exchanging fire with security forces, the International Maritime Bureau said.

The company said it believed over 3,000 tonnes of fuel had been removed.

"They did not ask for ransom, booty is what they were after. They also took the crew's valuables," said the company representative, who declined to be identified.

The Isle of Man-flagged vessel was seized 17 miles off the coast of the Togolese capital Lome, where it had reportedly been anchored, said Noel Choong, head of the IMB's piracy reporting centre.

The hijackers exchanged fire with a Togo navy patrol boat that answered a distress call but managed to elude the patrol by steaming off aboard the tanker, Choong said.

The Malaysia-based IMB has repeatedly warned ships plying the Gulf of Guinea to be vigilant and called on authorities to step up patrols, last year saying the region was emerging as a new piracy "hot spot".

The area has seen at least 36 attacks, including several hijackings, kidnappings and killings, so far this year.