In the weeks before the 11 September attacks, President George Bush was told by US intelligence that Osama bin Laden's terrorist network might hijack American planes, prompting the administration to issue a private warning to law-enforcement agencies, the White House acknowledged.
But officials said the president and US intelligence did not know that suicide hijackers were plotting to use planes as missiles, as they did against the World Trade Centre and the Pentagon.
"There has been long-standing speculation, shared with the president, about the potential of hijackings in the traditional sense," White House press secretary Ari Fleischer said. "We had general threats involving Osama bin Laden around the world and including in the United States."
He said the administration, acting on the information received in early August, notified the "appropriate agencies" that hijackings "in the traditional sense" were possible. The warning was never made public, he said.
The development, first reported by CBS News, comes as congressional investigators intensify their study of whether the government failed to adequately respond to warnings of a suicide hijackings before 11 September. It is the first direct link between President Bush and intelligence gathered before the attacks.
Mr Fleischer would not discuss when or how the information was given to President Bush, but a senior administration official, speaking on condition of anonymity, said the president was made aware of the potential for hijackings of US planes during one or more routine intelligence briefings last summer.
The CIA would not confirm what it told Bush, but the agency said the issue of bin Laden's attempting an airline hijacking was among a number of terrorist methods raised with government officials at the time.
But there was no information that suggested hijackers would crash planes into American landmarks and there was no mention of a date, a CIA official said. The information was based on intelligence obtained by the US government, he said.
Mr Fleischer said he did not know what agencies were notified or what they were told.
The Associated Press reported earlier this month that FBI headquarters did not act on a memo last July from its Arizona office warning there were a large number of Arabs seeking pilot, security and airport operations training in at least one flight school. The memo which urged a check of all flight schools to identify more possible Middle Eastern students.
A section of that classified memo also makes a passing reference to bin Laden, speculating that al-Qa'ida and other such groups could organise flight training, officials said. The officials said, however, that the memo offered no evidence bin Laden was behind the students that raised the concern.
Democratic Senator Bob Graham, the Senate Intelligence Committee chairman, said through a spokesman that the revelations in the memos marked an important discovery in Congress' investigation into why the FBI, CIA and other U.S. agencies failed to learn of and prevent the Sept. 11 plot.
"It represents a failure to connect the dots," said Sen.Graham's spokesman Paul Anderson. "This was dismissed rather lightly at FBI headquarters."
The FBI also has faced tough questioning about whether it failed to act aggressively enough after arresting Zacarias Moussaoui, a Frenchman of Moroccan descent, in August after he raised concerns by seeking flight training at a Minnesota flight school.
Moussaoui has emerged as the lone defendant charged in the aftermath of the attacks, which killed more than 3,000 people in New York, Washington and Pennsylvania. He is charged with conspiring with bin Laden and the 19 suicide hijackers to attack Americans.Reuse content