Reporting from Beirut -- In a dramatic and unprecedented show of prowess, suspected Somali pirates seized an oil tanker three times the size of a U.S. aircraft carrier deep in open seas, the U.S. military in the Middle East announced today.



The Liberian-flagged Sirius Star oil tanker was hijacked and its multinational crew of 25 kidnapped by pirates in the Arabian Sea on Saturday more than 450 nautical miles from Mombasa, Kenya, the Bahrain-based U.S. 5th Fleet said.



Typically, pirates attack within 200 miles of the shoreline and go after smaller prey, said U.S. Navy Lt. Nathan Christensen, adding that the pirates were "changing the way they're doing business" in the region.



"What this represents is a fundamental ability of pirates to be able to operate off the coast to an extent we have not seen before," Christensen said in a phone conversation from Manama, Bahrain, home to the 5th Fleet. "It's the largest ship we've seen attacked."



The giant oil tanker is owned by Saudi Arabia-based Saudi Aramco. Crew members include citizens of Britain, Poland, Croatia, Saudi Arabia and the Philippines, the Navy said. Christensen said the pirates have not made any demands yet.



The Sirius Star, manufactured in South Korea by Dubai-based Vela International Marine Ltd., is classified as a "very large crude-oil carrier," which typically cost about $120 million and can transport up to 2 million barrels of oil.



Piracy has become a scourge in the region with vessels hijacked at sea by assault-rifle-toting Somali bandits on high-speed watercraft. Piracy is another challenge to the already formidable tasks of fighting wars in Iraq and Afghanistan as well as against Al Qaeda militants that will be faced incoming U.S. Central Command chief Gen. David Petraeus in an area of operations that stretches from the Horn of Africa to Central Asia.



"As is evident with the attack on Sirius Star, increasingly daring attacks are being conducted by Somali pirates on a variety of merchant vessels," the 5th Fleet announcement said.



The U.S. Navy says it and other friendly forces have reduced successful piracy attacks from 53% in August to 31% in October. Last Tuesday, a British warship fended off an attack on a Danish commercial vessel, boarding the pirate ship and engaging in a gunbattle that resulted "in a number of fatalities," the announcement said.



"Our presence in the region is helping deter and disrupt criminal attacks off the Somali coast, but the situation with the Sirius Star clearly indicates the pirates' ability to adapt their tactics and methods of attack," Vice Adm. Bill Gortney, commander of the Combined Maritime Forces, was quoted as saying.



Gortney said military forces cannot be everywhere and urged commercial shippers to employ "self-protection measures" to defend themselves, including hiring private security contractors. Out of the last 15 piracy attacks, at least 10 failed to employ some kind of defensive mechanism, the Navy said.



"Companies don't think twice about using security guards to protect their valuable facilities ashore," he was quoted as saying. "Protecting valuable ships and their crews at sea is no different."