LONDON — Pirates have attacked and looted a tanker off the coast of Nigeria, taking five crew members hostage, the ship's operating company said on Wednesday.

Piracy and kidnapping in the oil-producing Delta and offshore are common, and West Africa's oil-rich Gulf of Guinea is second only to the waters off Somalia for the risk of pirate attacks, which drives up shipping insurance costs.

"On Monday the vessel [SP Brussels] was boarded by heavily armed pirates whist approximately 40 miles off the Niger Delta," Medallion Marine said in a statement. "The pirates ransacked the vessel for personal belongings and took five crew members with them on their departure."

Medallion Marine did not give the nationalities of those kidnapped or details of the ship's cargo.

The Nigerian Navy were not available for comment.