Armed men hijacked a Greek oil tanker off the coast of Nigeria at the weekend and took the 20 crew-members hostage, Greek port police told AFP Monday. \"We learned today (Monday) that the oil tanker \'Aegean Star\' belonging to the Endeavour Marine Agency company and flying a Liberian flag was hijacked Saturday, 30 nautical miles off the coast of Nigeria,\" a port authority press official said. \"For the moment, we don\'t have information on the condition of the crew,\" he added. The ship had set off from Ghana and was headed towards Benin, the same source said. The 20-person crew included three Greek nationals, including the ship\'s captain, authorities said. On Africa\'s opposite coast, pirates based in war-torn Somalia have become infamous for seizing ships in the Gulf of Aden and beyond, often demanding large ransoms in exchange for the release of the crew. A Greek-flagged oil-laden supertanker was seized off the coast of Oman by Somali pirates in February. The vessel and crew were released in April, although the company involved did not disclose if a ransom was paid.