"U.S. intelligence does believe that there are other suicide bombers out there who have been give missions to attack the United Sates and they have not been found," said ABC News consultant Richard Clarke.
Authorities told ABC News they received the information from accused Northwest airlines bomber, Umar Abdulmutallab. He provided the FBI with specific names and descriptions of others who trained with him in Yemen.
"There are also women who have been trained. So Al Qaeda is looking to put together an attack using people that would not fit a profile that we'd be looking for," said Clarke.
US officials say in one 48-hour period last weekend, six different people on the no-fly list were stopped from boarding US flights.
Two of them at London's Heathrow airport attempting to board flights on American Airlines to Miami and a United Airlines flight to Chicago.
The four others were stopped attempting to board flights in Nairobi, Kenya, the Caribbean island of Saint Maarten, in Fort Lauderdale and Minneapolis.
None was arrested or detained, although one was sent back to Saudi Arabia. However, authorities believe all six people were part of a well organized probe to find weak spots in the U.S. airline system.
At LAX's international terminal many travelers said they were unaware that security was focusing their attention on women.