The pirates on Monday sailed the Sirius Star, owned by Saudi oil company Aramco, to a Somali port in Eyl that has become a haven for bandits and the ships they have seized, a Navy spokesman said.
"This is unprecedented. It's the largest ship that we've seen pirated," said Lt. Nathan Christensen, a spokesman for the U.S. Navy's 5th Fleet. "It's three times the size of an aircraft carrier."
The ship is carrying its full load of 2 million barrels -- more than one-quarter of Saudi Arabia's daily output and worth over $100 million. The crew, from Britain, Croatia, the Philippines, Poland and Saudi Arabia, is reported to be safe, according to the BBC.
The supertanker was heading for the United States via the Cape of Good Hope at the southern tip of Africa, reported Reuters.
Christensen said the pirates hijacked the ship on Saturday about 450 nautical miles off the coast of Kenya - the farthest out to sea Somali pirates have struck.
Attacks off the Somali coast have increased more than 75 percent this year and Somali pirates have seized at least six several ships off the Horn of Africa in the past week, according to the Associated Press.
In September, pirates hijacked a Ukrainian freighter carrying military ammunition, grenade launchers and 33 Soviet-made tanks. The ship remains hijacked.
By expanding their range, Somali pirates are "certainly a threat to many more vessels," Christensen said. He declined to say if the U.S. Navy was considering taking action to rescue the tanker.
Warships from the more than a dozen nations as well as NATO forces have increased their military presence in recent months in response to the pirates, who have claimed up to $30 million in ransoms this year alone, according to the AP.
Northern Somalia's breakaway Puntland region, where Eyl is located, was on the lookout for the ship, according to Reuters, but authorities there have said they can do little to stop ships being seized.
War-torn Somalia has been without an effective government since warlords ousted President Mohamed Siad Barre in 1991 and then turned on each other.
The International Maritime Bureau, a piracy watchdog, said there had been 92 attacks off Somalia this year and 36 of the ships had been hijacked, reported Reuters. Fourteen ships are still controlled by pirates and 243 crew members are being held.
Graeme Gibbon Brooks, managing director of British company Dryad Maritime Intelligence Service, told the AP that the increased international presence trying to prevent attacks is simply not enough considering the area covers 2.5 million square miles.
"The coalition has suppressed a number of attacks...but there will never be enough warships," Brooks said.
