WASHINGTON (AP) — Intelligence officials are concerned about a new al-Qaida effort to create a bomb that would go undetected through airport security, according to a counterterrorism official, prompting the U.S. to call for tighter security measures Wednesday at some foreign airports.

The counterterrorism official, who would not be named because he was not authorized to discuss the matter publicly, declined to describe the kind of information that triggered this warning. But officials in the past have raised concerns about non-metallic explosives being surgically implanted inside a traveler’s body, designed to be undetectable in pat-downs or metal detectors.