The loaded tanker with 17 crew and a technician on board was hijacked on Sunday about 20 nautical miles off the port of Lome in Togo, said Noel Choong, head of the IMB’s piracy reporting centre based in Malaysia.
Pirates released the Panama-flagged vessel, which was transporting gas oil, 90 nautical miles off Lagos in Nigeria Thursday, Choong said.
None of those on board were injured, Choong added. He could not immediately give further details.
But Choong warned authorities and ships plying the area to be vigilant.
“We urge authorities in the area to beef up patrols to stop this menace,” he told AFP. “The pirates in this area are violent… We are warning ships to stay vigilant and maintain strict anti-piracy watches.”
The Gulf of Guinea off the west coast of Africa has seen 35 attacks, including several hijackings, kidnappings and killings, so far this year, Choong said.
Unlike in hijackings off the coast of Somalia on the opposite side of the continent, west African gangs usually target cargo, loading it onto other ships to sell on the black market.
Nigeria and nearby Benin launched joint patrols last year to address the problem.