Pirates have attacked an oil tanker off the coast of Nigeria and kidnapped two men, a Greek coast guard official said.

Ten pirates boarded the 18-crew ship, the 6,500 tonne Marshall Islands-flaggged MT ALTHE, and took its Ukrainian captain and Greek first engineer hostage late on Monday. 

They kidnapped the two men but did not touch the cargo (oil) or injure anyone.

Greek coast guard official

The attack took place 35 nautical miles off the oil-producing Niger Delta coastline, a Nigerian security source said.

The two hostages were taken away by speedboat to an undisclosed location. The rest of the tanker's men were robbed of personal items but were not hurt.

"They kidnapped the two men but did not touch the cargo (oil) or injure anyone," an official said.

The ship's manager, Piraeus-based Medtankers Management, confirmed the attack on Tuesday.

"We are doing everything we can for their release," an official said, adding that so far, no demand for ransom had been received.

Pirate attacks off the coast of Nigeria have increased by a third this year. West Africa's Gulf of Guinea is a target for gangs wanting to steal cargo.

Unlike Africa's east coast, where ships are protected by armed guards, ships passing through the Gulf of Guinea have little protection.

Sailors and oil workers taken hostage in Nigerian waters are usually released unharmed once a ransom has been paid.

The Nigerian navy is conducting an investigation into the attack, a spokesman said.

Source: Reuters