Law enforcement, airline personnel and airport security officials were warned on Tuesday to pay close attention to electronic items being carried aboard airplanes, with the explanation that Al Qaeda had been working on new methods of concealing weapons.
The advisory advised screeners to take extra care when checking common items like cell phones, portable stereos and even camera flash devices. Homeland security officials earlier told Fox News that terrorists might try to "weaponize" electronic items.
The officials cautioned that the warning was not especially new, but that more specific intelligence had been received that would be useful to airline screeners.
"Recent reporting indicates Al Qaeda (search) may attempt to modify common electronic items carried by air travelers, such as cameras, for use as weapons in order to circumvent improved security screening," the advisory states.
"It is also possible that these weapons could be designed for use against government buildings, and/or public venues having controlled access, and security screening checkpoints," it adds.
Al Qaeda operatives have shown a "special interest," the advisory said, in converting a camera flash attachment into a stun-gun type of weapon or improvised explosive device. Another experiment apparently focused on disguising explosives and a detonator inside a camera.
Other possible "weaponizable" items included remote door or lock openers, cellular telephones, multi-band radios and dual-speaker radios. Screeners should inspect those or similar items, the advisory says.
An earlier advisory, released July 29, warned that Al Qaeda might try to repeat the Sept. 11, 2001 airline hijackings.
"The hijackers may attempt to use common items carried by travelers, such as cameras, modified as weapons," last week's advisory read, adding that hijackers with pilot training might no longer be needed to take over airplanes.
A suspect in the May 12 bombings in Saudi Arabia (search) also told interrogators last week about new plots to hijack planes and use them as weapons, but intelligence officials said he might have been lying.
On Monday, a CIA official said that the audiotape purported to be from Al Qaeda leader Ayman al-Zawahri (search) and broadcast over the weekend on an Arab satellite television channel was probably authentic.
Al-Zawahri, Al Qaeda's organizational chief and second only to Usama bin Laden, warned that the United States would pay dearly if Muslim detainees at Guantanamo Bay were harmed.
A copy of the July 29 warning said an Al Qaeda attack could take place by the end of the summer. It suggested cities on the East Coast of the United States, in the United Kingdom, Italy and Australia as possible targets.
"No equipment or operatives are known to have been deployed to conduct the operations," the warning said.
The State Department also updated its "Worldwide Caution" advisory in late July to include the information from the homeland security warning.
"The U.S. government remains deeply concerned about the security of U.S. citizens overseas," the State Department advisory said. "U.S. citizens are cautioned to maintain a high level of vigilance, to remain alert and to take appropriate steps to increase their security awareness."
The national terrorist threat level stands at yellow, signifying an elevated risk of attacks. The five-level, color-coded system was last raised to orange, or high risk, for 11 days in May. DHS officials have said there are no current plans to raise the alert status..
Since the Sept. 11, 2001, attacks, Congress has taken a number of actions to limit the possibility of suicide hijackings, including arming commercial pilots, boosting the number of air marshals and hiring an all-federal work force to screen airline passengers.
Fox News' Mike Emanuel, Teri Schultz and Anna Stolley and The Associated Press contributed to this report.