U.S. security officials are warning of terrorist plans to hide bomb components in shoes.
The CBS television network has obtained a copy of the warning, issued Wednesday by the Department of Homeland Security and the FBI.
The general terrorism-related awareness notice was prompted by the discovery in Europe last month of a pair of shoes used to smuggle electric blasting caps across international borders.
The thick soles of the shoes were hollowed out to hide the caps.
The U.S. warning notes that standard visual inspection of the shoes would probably have missed the contraband. The report notes that while all footwear at U.S. airports must go through an x-ray machine, many other nations have no such requirement.
The FBI and Homeland Security Department add that there is no specific, credible intelligence that terrorists plan to use the tactic in the United States.
In December 2001, shortly after the September 11th attacks, would-be shoe-bomber Richard Reid attempted to blow up a transatlantic flight with explosives concealed in his shoes.
The al-Qaida operative was tackled by fellow passengers as he tried repeatedly to light a fuse attached to one shoe. He is now serving a life sentence at a U.S. maximum security prison.