At least two of the groups of hijackers who commandeered US airliners yesterday, were armed with knives, according to the US Attorney General Mr John Ashcroft.
"American Airlines flight 11 departing Boston to Los Angeles, was hijacked by suspects armed with knives," Mr Ashcroft said this morning.
"This plane crashed into the World Trade Center."
Earlier, CNNreported that Barbara Olson, wife of US Solicitor General Mr Ted Olson, made two mobile telephone calls from the hijacked Boeing 757 that crashed into the Pentagon, saying the hijackers of that aircraft were armed with knives and knives for cutting cardboard.
Mrs Olson, also a well-known television political commentator, was one of the 64 people who died in the crash.
A spokesman for Mr Olson said she had not even been due to fly on the fight.
"She was not even supposed to be on that flight. She flew a day early to make sure she could be at Ted's birthday," said the spokesman.
"She called and said she was locked in the toilet and the plane had been hijacked.
"She said they had box-cutters and knives. They had rounded up the passengers at the back of the plane.
"She referred to them as more than one. There was nothing she could do. She said to her husband: 'What do I do?'"
The call ended seconds before the crash itself.
Her husband, who had been President Bush's lawyer during the legal battle over the disputed presidential election, was said to be "distraught" at her death.
A passenger on the aircraft that crashed outside of Pittsburgh, Pennsylvania locked himself in one of the plane's toilets and called emergency services from his cell phone to report the hijacking.