LAGOS: A Nigerian naval ship freed an oil tanker on Wednesday that had been hijacked near its biggest city Lagos, the navy and the managers of the vessel said.

Pirates hijacked the Singapore-registered Abu Dhabi Star late on Tuesday, about 14 nautical miles from the entrance to Lagos port, the navy said, adding that crew members had hidden in a room on the ship.

The raiders escaped when they saw a Nigerian naval ship and naval helicopter approach, navy spokesman Commodore Kabir Aliyu said.

“There was no exchange of fire. All the crew members are safe,” he said. The rescued ship would anchor at Lagos harbour under naval protection pending an investigation, he added.

A security source said there were 22 Indian sailors on board.

Lieutenant Commander Jerry Osomara, the Nigerian navy's spokesman for Lagos, said it was not known if the fuel on board had been stolen.

“Definitely their intent was to steal the oil, but we don't yet know if they were successful,” he said.

Earlier, an official at security firm AKE suggested the tanker had been laden with fuel, and speculated the pirates may have planned to offload it into a waiting vessel and sell it on the region's illegal fuel market.

Piracy off Nigeria and other countries in West Africa's oil-rich Gulf of Guinea is on the rise, and the region is second only to the waters off Somalia for the risk of pirate attacks, which drives up shipping insurance costs.

Piracy nets huge sums for armed gangs in the region from stolen cargo, although unlike their Somali counterparts they rarely ask for ransoms, releasing crew as soon as they have looted a vessel.

The Abu Dhabi Star's management company, Dubai-based Pioneer Ship Management, confirmed the rescue.

“Pioneer Ship Management would like to thank the Nigerian Naval Authorities ... for responding so professionally to this criminal act and are thankful that all the seafarers are now safe,” it said in a statement.

A Greek-operated oil tanker seized off Togo at the end of last month was tracked down on Wednesday off the coast of Nigeria after pirates had abandoned it. AKE said some 3,000 tonnes of gas oil, worth about $3 million at market value, was stolen.