The Federal Bureau of Investigation has put law enforcement agencies in the United States on high alert and asked them to look out for subtle signs or body language to track down possible suicide bombers, a media report said.
A "lightly classified" bulletin sent to 18,000 law enforcement agencies asks them to look for obvious signs of trouble -- people wearing heavy, bulky jackets on warm days, smelling of chemicals, trailing wires in their jacket as also for more subtle one such as tightly clenched fists, Time magazine reported.
"Someone who never shows his palms could be gripping a detonator rigged to go off when a button is released," it said.
The magazine said the bulletin, headlined 'Possible suicide bomber indicators', was distributed via the FBI'S secure Law Enforcement Online Intranet.
The report also notes that suicide bombers may disguise themselves in stolen military, police or firefighter's garb, or even as pregnant women.
Time quoted FBI sources as saying there's no hard intelligence warning of specific plans by terrorists to launch suicide attacks.
The circular was prompted by "a renewed concern" that fury at the US for its occupation of Iraq or its support of Israel could move some extremists to attempt to bring the war to the American homeland, the magazine said quoting one official.
"At the end the day, it's probably one of the simplest forms of attack, and it's one of the hardest to detect," one counter-terror veteran told Time.
