ABIDJAN, Ivory Coast — Armed men have hijacked a tanker carrying 5,000 tons of oil from an Ivory Coast port and taken it off the coast of Ghana, though its precise whereabouts are unknown, government authorities and maritime officials said Monday.

The vessel ITRI was seized Wednesday as it was preparing to deposit oil at the port of Abidjan, Ivory Coast’s commercial capital, according to the Ivory Coast government, which communicated for the first time on the case Monday.