The US government was warned eight years ago that the Pentagon and White House were vulnerable to attack from hijacked jets, a military adviser has claimed.
Dr Marvin Cetron said he prepared a 250-page report for the US intelligence agencies in 1993 that detailed his concerns butit was ignored.
"I said look, you've got a major problem here with aircraft, they could hit the White House or the Pentagon - it's a simple matter of coming in and making a left turn at the Washington Monument and running directly into the White House, or a right turn and going into the Pentagon," Dr Cetron told BBCtelevision.
"They understood and they ignored it, they took it out of the final draft," he said.
"I think the reason they didn't want that published is because they felt they couldn't do anything about it. It would scare people and the flying public, which it probably would have, and therefore why worry about it - out of sight, out of mind".
Republican Senator Mr Wayne Allard, a member of the US administration's armed forces committee, told the BBC's Newsnighthe was part of various hearings where the suggestion of possible attacks from hijacked jets were made.
He said the warnings were similar to the events on Tuesday that saw four planes hijacked to deadly effect.
Asked how clear were the warnings he got while sitting on the intelligence committee, he said: "They weren't clear, they were just speculations. They were suggestions of what could happen".
PA