Al-Qaeda considered attacks on US oil and gas infrastructure as late as last year, according to documents seized from its ex-leader Osama bin Laden's compound, officials said Friday.
But officials were also quick to stress that there was no specific or imminent threat to the United States, noting it was unclear whether Al-Qaeda had pursued these plots after 2010.
In a confidential intelligence warning, the FBI and the Homeland Security Department provided information on "Al-Qaeda's interest in targeting oil and natural gas infrastructure," DHS spokesman Matt Chandler said in a statement.
"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," he added.
"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 mid-last year."
The warning was sent to federal, state and local law enforcement, along with oil and gas firms, but the national terror threat level was not raised.
The Homeland Security Department issued a similar warning on May 5 over potential terror plots targeting US trains on the upcoming 10th anniversary of the September 11, 2001 attacks, citing other documents found at bin Laden's hideout.
Details about the plot came from documents seized during the dramatic May 2 US commando raid on bin Laden's compound deep in Pakistan, a US official said on condition of anonymity.
"No specific attack method was identified in 2010 and there was no reference to a specific date or time of the threatened attack," the official added, noting that oil tankers have long been an Al-Qaeda target.
In October 2002, a small boat laden with explosives rammed into the French supertanker Limburg off Yemen's southeastern coast, killing one crew member and sending more than 90,000 barrels of oil pouring into the Gulf of Aden.