PIRATES attacked a Greek-owned oil tanker off Nigeria Friday but failed to hijack the ship after the crew hid in a safe room, the International Maritime Bureau said.The tanker was anchored off Lagos when armed pirates boarded early on Friday, said Noel Choong, head of the IMB’s piracy reporting centre in Kuala Lumpur.The 23 crew onboard managed to lock themselves into a safe room and sent out a distress call that was received by the IMB, which in turn alerted the Nigerian navy and other warships patrolling the area, Choong said.Safe rooms are increasingly used by shipping firms to protect crews and thwart pirate attacks.Choong said the pirates, likely aiming to steal the ship’s cargo, abandoned their plan as they could not enter the safe room and urged crews of other ships off west Africa to be vigilant."The area remains risky,” he told AFP. "We urge all ships to maintain strict anti-piracy watches,” he said.At least 21 attacks in the Gulf of Guinea off the west coast of Africa have taken place this year, with four vessels hijacked, according to Choong.Two seafarers have been killed, two injured and three kidnapped, he said. Nigeria, Africa’s largest oil producer, was targeted in 13 out of the 21 attacks, Choong said.Unlike in hijackings off the coast of Somalia on the opposite side of the continent, west African gangs have not sought ransoms, instead unloading cargo onto other ships to sell on the black market.Nigeria and nearby Benin launched joint patrols last year to address the problem.