"The boat was hijacked in international waters," said Alexis Guie, who is in charge of
communications at the port.
The International Maritime Bureau had said earlier that a French tanker disappeared at the weekend off the west African country, apparently in an act of piracy.
The ship was sailing under a Luxembourg flag according to the French government and had a crew of 19 Togolese sailors.
The Luxembourg government said it had been informed of the incident on the tanker ship Gascogne by the French group Sea-Tankers, who own the vessel.
"When a boat is hijacked more than 300 kilometres from the Ivorian coast, that can't be in our waters," Guie said, adding that Ivorian authorities had "no information" about the incident.
"It appears pirates are moving towards the Ivory Coast because Nigeria and Benin have increased patrols in the Gulf of Guinea," said Noel Choong, of the International Maritime Bureau, who declined to elaborate on the incident.
He expressed concern over a recent spate of incidents in the area, revealing two other attacks on merchant ships in recent days, one of which left a seafarer with gunshot wounds.
Choong also said a suspected pirate mother ship was sighted during an attack off Nigeria on January 31.
With five incidents recorded so far this year, Choong said attacks in the area "are happening more frequently than before."
The Gulf, which includes waters off Nigeria, Africa's largest oil producer, has emerged as a new piracy hotspot, with 62 attacks recorded in 2012, including hijackings, kidnappings and killings.
Pirates usually target fuel cargo, loading it onto other ships to sell on the lucrative black market, rather than seeking a ransom to release ships.