The United States navy says the hijacking of a giant Saudi oil tanker in the Indian Ocean by Somali pirates is unprecedented and marks a fundamental shift in their capabilities.
The Sirius Star is carrying its full load of 2 million barrels - more than a quarter of Saudi Arabia's daily output. Its international crew of 25 is said to be unharmed. The ship is the biggest yet seized by Somali pirates.
It was attacked 800 kilometres off the coast of East Africa and is now on a course towards the port of Eyl in northern Somalia. It was sailing under the Liberian flag at the time.
The chairman of the US Joint Chiefs of Staff, Admiral Mike Mullen, says the pirates are well trained.
Attacks on shipping off the Horn of Africa and Kenya by pirates, who are mostly Somali, prompted foreign navies to send warships to the area this year.
Figures from the International Maritime Bureau show that attacks in the area - the Gulf of Aden and the Indian Ocean off the African coast - made up a third of all piracy incidents worldwide in 2008.
In the first nine months of the year, 63 incidents were reported. As of 30 September, 12 ships remained captive and under negotiation, with more than 250 crew being held hostage.
The 330-metre ship is owned by the Saudi company Aramco and was built in South Korea's Daewoo shipyards. It made its maiden voyage in March 2008.