The FBI has produced the first piece of evidence linking the suicide hijackers who carried out the attacks on the US.
A letter of instruction and guidance written in Arabic, has been found in the luggage of two men involved in the attacks on Washington and New York.
A third copy was found at the site in Pennsylvania where one of the hijacked planes crashed.
The letter urged hijackers to smile at taxi drivers and to ensure that no one was following them.
US Attorney General John Ashcroft said the letters were a chilling insight into the terrorists’ mindset.
The revelations came as the UN Security Council adopted a sweeping counter-terrorism measure that demands all nations to freeze finances belonging to terror suspects or any organisation aiding them.
The US-sponsored strategy also requires countries to deny safe haven to anyone responsible for, or supporting, terrorist attacks.