A vessel has been hijacked by pirates off the coast of Nigeria and for the first time two crew members have been taken hostage, with one still unaccounted for.

The attack on the 1991-built, 5,900 dwt reefer Breiz Klipper is the seventh in this region in the first two months of 2012 compared with 10 attacks in the whole of last year. An International Maritime Bureau spokesman said this signalled an alarming rise.

However, he said the model employed by pirates in Nigeria was nothing like that used in Somalia, as the crew had been taken off the ship.In the Gulf of Aden the unique political situation allows pirates to keep hostages on vessels for extended periods of time.

The spokesman also said that the Nigerian attacks were “unacceptably violent”.

It is unclear whether the pirates intend to hold the crew members of the Curacao-flagged vessel to ransom. The IMB is awaiting updates from the owners.

The ship’s manager, Seatrade, reported that the attack occurred at approximately 1600 hours yesterday.

The company said armed pirates used force to board the ship and took valuables from crew members and the vessel’s safe.

Seatrade said it regretted to confirm that on leaving the ship the attackers took two of the ship’s crew hostage while a third crew member is still unaccounted for.

One of the crew members has sustained minor injuries and is being given medical treatment on board the ship. The vessel, carrying frozen fish, is steaming off the West African coast awaiting further instructions.

Seatrade said it would work closely with the local authorities and professional advisers to secure the earliest release of its crew.