Washington (CNN) -- The Department of Homeland Security and the FBI have warned police across the United States that al Qaeda has a "continuing interest" in attacking oil and natural gas targets, a department spokesman said Friday.
The warning issued Thursday came as a result of information seized during the May 2 raid that killed Osama bin Laden in Pakistan, a U.S. official said.
"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.
"However, in 2010 there was continuing interest by members of al Qaeda in targeting oil tankers and commercial oil infrastructure at sea."
It is "unclear if any further planning has been conducted" since the middle of last year, Chandler said.
CNN obtained a copy of a DHS/FBI intelligence bulletin that says al Qaeda has been interested in "targeting unspecified oil tankers abroad" as a means to "draw the West into an extreme economic crisis" by disrupting a significant portion of the oil supply for several years.
The advisory says al Qaeda wanted to target oil tankers in the Indian and Atlantic oceans, as well as the Arabian Sea, but the terrorist group "was opposed to targeting tankers in coastal areas with large Muslim populations."
The warning says al Qaeda "believed an effective method for sinking oil tankers was to hijack them and then detonate explosives from the inside." The group thought it would be more difficult to stage an attack from outside a ship, as it could "require several explosive charges since tankers are divided internally into multiple watertight sections."
The bulletin says in 2010 al Qaeda tried to get information about the size, layout and construction of oil tankers to help with attack planning. The document says al Qaeda also recognized the importance of pre-attack surveillance of a possible target and recommended conducting trial runs.