"Mobil Producing Nigeria, operator of the joint venture with the Nigerian National Petroleum Corporation, confirms that in the early hours of Monday October 17, 2011, some armed men attacked a third party vessel near our facilities, offshore Akwa Ibom State," a company statement said on Tuesday.
"At this time, we do not know the identity of the attackers, nor reason for their action. The incident has been reported to security and relevant government agencies."
The company did not say if anyone had been kidnapped or what happened to the vessel.
A sailor was kidnapped from a ship supplying an Exxon oil platform in the same region on Sep. 30. There has been no update on his whereabouts.
Pirates last week released a ship seized off the coast of Nigeria, freeing the 20-member Eastern European crew who had been held for five days. There was no confirmation from the owners of the ship about a ransom payment.
The incident was the latest in a string of attacks on ships in the Gulf of Guinea that experts say is threatening an emerging trade hub and growing source of oil, metals and agricultural products to world markets.
Pirates in the Gulf of Guinea, which stretches from Guinea to Angola, tend to raid ships for cash and cargo rather than hijacking the crews for ransom like their counterparts off the coast of Somalia.