According to one high placed US official, concern focuses on the possibility of terrorists carrying explosive devices implanted inside their bodies.
Counter terrorism sources add that plastic explosives in the body of a would-be suicide bomber without metal components are undetectable by standard screening devices such as those used at most international airports.
It has been suspected for some years that doctors and surgeons in Yemen in the service of Al Qaeda in the Arabian Peninsula were experimenting with implanting of plastic explosive devices inside the bodies of suicide bombers or even animals. According to Western counter terrorism sources, the surgeon would open the abdominal cavity and implant the explosive device among the bomber's internal organs.
Some US sources are calling the current threat the most serious since 9/11. They are alarmed by the degree of confidence AQAP leaders show in openly using electronic communications to boast about the unstoppable attack they are plotting.
A senior US official described the terrorists as saying the planned attack is "going to be big" and "strategically significant."
BTW in other area news... It appears Jomo Kenyatta airport was closed after the international arrivals hall had a big fire.