“I can confirm the incident. It was on Sunday morning,” said Corrie van Kessel, a spokeswoman for Sea Trucks Group, which owns West African Ventures Limited, operator of the vessel.
“12 crew members … There is a big rescue operation in progress at the moment,” she added, specifying the 12 missing were the vessel’s entire crew.
She could not confirm the nationalities of the sailors aboard the Jascon 4, which sank off southern Nigeria’s Escravos, the site of a Chevron oil terminal.
Nigeria is Africa’s biggest oil producer, with Chevron among the major operators in the country.
Van Kessel said it was not yet clear what caused the accident. The vessel had been involved in towing operations for a tanker, she said.
A Nigerian navy spokesman did not immediately respond to phone calls.
US-based Chevron issued a statement confirming the tug had sunk, but referred all questions on the crew to West African Ventures Limited.
Chevron said the vessel “capsized and sank early in the morning of May 26 while supporting a tanker loading at SBM 3, a loading point 30 kilometres (18 miles) offshore in the Escravos area of Delta state, Nigeria.
“Initial reports indicated that heavy ocean swells caused the Jascon 4 to capsize while performing tension tow operations of the tanker at SBM 3.
“Emergency response has commenced, including search and rescue operation with surface vessels, helicopters and divers.”
Chevron gave no further information on the cause of the accident.
Nigeria’s treacherous and busy offshore waters see regular incidents, including accidents as well as pirate attacks and kidnappings.
An inferno at a Chevron natural gas well off Nigeria that began in January 2012 and which killed two people and sparked fears of serious environmental damage stopped burning only in March 2012.