ABC's Jonathan Karl reported on This Week Sunday the intercepted al-Qaeda communications that led to the closings of more than 20 U.S. embassies across the Muslim world described a planned attack as "big" and "strategically significant:"
"The part that is alarming is the confidence they showed while communicating and the air of certainty," the official said, adding that the group — Al-Qaeda in the Arabian Peninsula — appeared to have a media plan for after the attack.
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Authorities do not know the exact target of the planned attack, according to the official.
"We do not know whether they mean an embassy, an airbase, an aircraft, trains," the official said.
The official said there is concern about devices that could be implanted inside the body of a terrorist.
"We are concerned about surgically implanted devices," said. "These are guys who have developed the techniques to defeat our detection methods."