Militants are showing renewed interest in using a surgically implanted bomb to blow up a commercial flight, though there is no indication an attack is imminent, a US security official said, citing new intelligence.
US authorities have warned their counterparts abroad as well as air carriers about the new information and were taking steps to boost security.
"The Department of Homeland Security has identified a potential threat from terrorists who may be considering surgically implanting explosives or explosive components in humans to conduct terrorist attacks," the advisory to foreign counterparts said, according to the US security official.
Such a threat is likely to come from overseas rather than domestically, but precautions were being taken on both sides, the official said on condition of anonymity.
The new intelligence did not indicate an attack was imminent, the official said.
US authorities have been on high alert after American forces killed Al Qaeda leader Osama bin Laden in May, ramping up security at airports, government buildings and other facilities in case of a retaliatory strike.
The official declined to say whether the new intelligence came from documents collected at the compound in Pakistan where bin Laden was found and killed.
The possibility of a suicide bomber attacking with explosives implanted in the person's body has long been a concern for authorities and a difficult threat to detect.
In the past, attacks involved explosives packed in luggage, shoes, clothing or other items. A Nigerian man was arrested in December 2009 and has been accused of trying to ignite a bomb hidden in his underwear aboard a flight from Amsterdam to Detroit. In October, toner cartridges packed with explosives were sent aboard US-bound cargo planes but were intercepted and defused overseas before they exploded.
In the wake of such attacks, US aviation security authorities have steadily ramped up passenger and cargo screening, requiring travelers to have their shoes X-rayed, go through full-body scanners and restricting liquids allowed in the passenger cabin of planes.
Transportation Security Administration spokesman Nicholas Kimball said passengers flying into the United States may notice enhanced security measures, including talks with them as well as pat-downs and the "use of enhanced tools and technologies."