WASHINGTON (AP) -- Osama bin Laden's personal files revealed a brazen idea to hijack oil tankers and blow them up at sea last summer, creating explosions he hoped would rattle the world's economy and send oil prices skyrocketing, the U.S. said Friday.
The newly disclosed plot showed that while bin Laden was always scheming for the next big strike that would kill thousands of Americans, he also believed a relatively simpler attack on the oil industry could create a worldwide panic that would hurt Westerners every time they gassed up their cars.
U.S. officials said the tanker idea, included in documents found in the compound where bin Laden was killed nearly three weeks ago, was little more than an al-Qaida fantasy. But the FBI and Department of Homeland Security issued a confidential warning to police and the energy industry Friday. The alert, obtained by The Associated Press, said that al-Qaida had sought information on the size and construction of oil tankers, had decided that spring and summer provided the best weather to approach the ships, had determined that blowing them up would be easiest from the inside and believed an explosion would create an "extreme economic crisis."
"We are not aware of indications of any specific or imminent terrorist attack plotting against the oil and natural gas sector overseas or in the United States," Homeland Security spokesman Matthew Chandler said in a statement Friday. "However, in 2010 there was continuing interest by members of al-Qaida in targeting oil tankers and commercial oil infrastructure at sea."
With about half the world's oil supply moving on the water, industry and security experts have warned for years that such an attack would be a jolt to global markets. That's particularly true if terrorists carried it out in one of the narrow waterways that serve as shipping chokepoints.
"You start blowing up oil tankers at sea and you're going to start closing down shipping lanes," said Don Borelli, senior vice president of the Sufan Group security firm and a former FBI counterterrorism agent in New York. "It's going to cause this huge ripple through the economy."
Still, even if al-Qaida were able to blow up one of the supertankers that move oil around the globe, it would barely dent the world's oil supply, said Jim Ritterbusch, president of Ritterbusch and Associates, who has been trading oil contracts since the futures market opened on the Nymex in 1983. A tanker holds about 2 million barrels, or enough to supply world demand for about a half hour.
The terrorist threat to oil infrastructure is nothing new. Members of a British terror cell that hoped to hijack trans-Atlantic airplanes in 2006 had also made plans to attack oil and gas targets in Britain. And al-Qaida's franchise in Yemen has attacked pipelines.
Friday's alert was significant mostly because it linked the scheme directly to bin Laden, meaning the idea probably has circulated among al-Qaida's most senior leaders.
The government encouraged companies to continue random screening, to warn employees about possible threats and to establish procedures for reporting suspicious activity. But there was no immediate effect on oil markets, and both shippers and security officials said it was business as usual on the water.
"This has been a possibility on everyone's minds for some time now," said Bill Box a spokesman for the International Association of Independent Tanker Owners. "Everyone is aware of what might happen."
Shippers have been on particular alert as threats of piracy have increased along the African coast. In 2008, Somali pirates captured the Sirius Star supertanker and held it for ransom. In 2007 the Japanese tanker the Golden Nori was hijacked carrying 40,000 tons of the highly explosive chemical benzene. Intelligence officials initially worried that terrorists might try to crash the boat into an offshore oil platform or use it as a gigantic bomb, but it proved to be another attack by pirates seeking ransom.
Then in 2010, two groups of pirates got into a shootout while arguing over the ransom for the Maran Centaurus, threatening to turn the ship into a massive fireball.
Pirates have had success with a relatively low-tech strategy. They fire at a ship to get it to slow down, then pull alongside in skiffs. Using lashed-together ladders or grappling hooks, the pirates climb on board with guns. Many ship owners are reluctant to have armed guards onboard, since the cargo is so flammable that sailors are even forbidden to smoke.
Somali pirates take the ships for money. The information taken from bin Laden's compound after he was killed May 2 suggests al-Qaida was interested in adapting that strategy to terrorize.
The U.S. has warned for years that such an attack in a narrow waterway, such as the Strait of Hormuz between Oman and Iran, would immediately send oil prices higher.
In Asia, concerns have centered on the continent's key oil chokepoint, the Strait of Malacca, located between Indonesia, Malaysia, and Singapore. Last year, an Indonesian al-Qaida affiliate set up a training camp at the beginning of the strait, leading to speculation about an attack there and prompting Singapore to issue a warning.
"The good thing is that boats don't move that fast. It gives you plenty of time to interdict," said Crispian Cuss, the program director at Olive Group, one of the biggest private security companies in the Middle East. "If a vessel was hijacked by an al-Qaida organization and headed toward a major port, the authorities would not let that vessel get anywhere near that port."
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Sullivan reported from Detroit. Associated Press writers Chris Kahn in New York; Cassandra Vinograd, Raphael Satter, David Stringer and Meera Selva in London; Chris Brummitt in Islamabad, Pakistan; Kimberly Dozier in Washington and Katharine Houreld in Nairobi contributed to this story.