A secret Pentagon unit had Mohammed Atta, the 9/11 ringleader, in its crosshairs 13 times before the 2001 attacks, a US congressman has claimed citing the unit's records.
Curt Weldon, a Republican representative, said on Tuesday data produced by the US military intelligence unit code-named Able Danger showed Atta's name 13 times.
The unit used data mining to investigate the al-Qaida network.
Weldon said: "Thirteen times we have hits in the data that's still available, that we were told was destroyed."
Weldon cited recent analyses of data gathered by Able Danger before the 2001 attacks on New York and Washington.
"They knew he was up to no good and that he was planning something."
Weldon, vice-chairman of the House Armed Services and Homeland Security Committee, spoke on the eve of a House Armed Services joint subcommittee hearing on Able Danger which he has initiated.
The House representative has pressured Congress and the Pentagon to investigate Able Danger since August, arguing that government officials became aware of Atta's ties to al-Qaida earlier than admitted.
The USS Cole attack could have
been prevented, says Weldon
Weldon said he now had proof there had been several attempts to transfer the information to the FBI, but they were blocked by lawyers for the administration of George Bush.
He said: "We have information that will be testified to under oath that there were attempts to transfer information to the FBI on at least three occasions, and on all three of those occasions in September of 2000, lawyers within the administration denied those meetings from taking place."
At least one witness will testify under oath that Atta had been on the US intelligence radar before the attacks, Weldon said.
"At least one additional witness has come forward who just retired from one of the intelligence agencies who will also testify under oath that he was well-aware of, and identified, Mohammed Atta's both name and photo prior to 9/11 occurring."
Weldon also said that Able Danger had detected problems in Yemen, which if they had been properly communicated, could have prevented the attack on the USS Cole in the Yemeni port of Aden in October 2000.
The lawmaker has criticised the official investigative panel on the 9/11 attacks as lacking, and for months has alleged that the authorities were trying to hide pre-September 11 errors committed in tracking al-Qaida to protect senior officials.
The issue has reopened a long-standing controversy over the failure of the US intelligence agencies to share information that might have prevented the September 11 attacks.