Gunmen seized a Nigerian-owned, Panama-flagged tanker with 16 Nigerian crew off Ivory Coast's port of Abidjan as it prepared to unload 5,000 tonnes of fuel, port officials said on Monday.Gunmen seized a Nigerian-owned, Panama-flagged tanker with 16 Nigerian crew off Ivory Coast's port of Abidjan as it prepared to unload 5,000 tonnes of fuel, port officials said on Monday.