Bags containing the box cutters and some other suspicious items were found in the lavatories of two jets belonging to Southwest Airlines, leading federal authorities to order a search of every commercial airliner in the United States.

But law enforcement officials say notes were also found on the planes urging whoever discovered the items to alert authorities about how what is supposed to be stepped up airport security failed to detect such objects before they were smuggled aboard.

Apparently because of that, FBI Director Robert Mueller does not, at this stage at least, suspect the find was part of possible plot to hijack or sabotage airliners.

"What I will tell you is there does not appear to be an imminent threat, it does not seem to be a terrorist act and we are in the middle of the investigation," he said.