Nigeria pirate attack: US sailors seized Published duration 24 October 2013

image copyright AFP image caption Nigerian navy special forces patrol the coast against attacks by pirates

Pirates have seized two US sailors from an oil supply ship off the coast of Nigeria, officials say.

The captain and chief engineer of the US-flagged C-Retriever were taken on Wednesday by armed men who stormed the boat, they said.

US officials said it was not a terrorist act, but were concerned about the rise in piracy off West Africa.

In kidnaps in the region, crew members are normally freed unharmed after any oil on board the ships is stolen.

US State Department Deputy Spokeswoman Marie Harf Wednesday's incident was being treated as "an act of piracy" rather than terrorism.

Gunmen attacked the C Retriever, an oil supply vessel, near the coastal town of Brass in Nigeria's oil rich Bayelsa State.

The chief engineer and the captain, both American citizens, were kidnapped. The vessel and 11 other members of the crew were reportedly released.

'Lucrative crime'

White House spokesman Jay Carney told reporters: "We are concerned by the disturbing increase in the incidence of maritime crime, including incidents of piracy off the coast of West Africa, specifically in the Gulf of Guinea."

The International Maritime Bureau has recorded more than 40 attacks in the area this year with 132 crew taken hostage. The gangs usually target the oil vessels to steal the cargo.

"Pirate networks in the Gulf of Guinea are focusing on product theft from tankers and this relatively new type of crime has evolved into a unique and highly lucrative form of maritime crime," said the Risk Intelligence security firm, in its October report

It is estimated that oil product worth approximately $100m (approximately £62m) has been stolen since 2010.

In recent months there have been numerous kidnappings of foreign oil workers and wealthy Nigerians, especially in the oil-producing Niger Delta region.

They have often been held until a ransom payment is made.