"Recent intelligence indicates that terrorists continue to develop plans to hijack aircraft and use them as weapons, despite enhanced worldwide airport security and increased vigilance on the part of passengers and crew members since the September 11 attacks," the FBI warned in its weekly bulletin sent to law enforcement agencies, according to a Fox News report.
"Intelligence indicates terrorists are considering the use of improvised explosive devices (IEDs) assembled onboard to hijack an aircraft or, alternatively, destroy it over heavily populated areas in the event of passenger or crew resistance," the bulletin added.
The FBI noted that components of IEDs can be smuggled onto planes concealed in clothing or personal carry-on items.
Retired U.S. Air Force Col. Darrel Whitcomb said, "We are once again very aware of the fact that the enemy realizes how important aviation is to us as a nation and once again they're going to try to use it against us."
"That's what they did on 9/11 -- they took those beautiful airplanes that we were comfortable with and turned them against us," Whitcomb added.
The bureau told law enforcement officials and security personnel to "remain vigilant for attempts, possibly involving one or more individuals, to smuggle IED components onboard aircraft."
