Robert Mueller, the FBI's director, said there was evidence that one or more of the hijackers had contacts with the al-Qa'ida network of Osama bin Laden, adding that the FBI was following up more than 200,000 leads.
Investigators released a new set of photographs yesterday of the 19 men alleged to have hijacked the four US aircraft as part of a "national neighbourhood watch" designed to gather information.
Though some photographs of the men have been in circulation for almost two weeks, most of the ones issued by the FBI are clearer. Six of the photographs have not been released before and a further six are versions or replacements of photographs previously issued. The agency said there are still doubts as to the true identity of some of the men.
: "What we are currently doing is determining whether, when these individuals came to the United States, these were their real names or they changed their names for use with false identification in the United States."
Some of the names released yesterday have slightly different spellings and others have additional names added, compared with the initial list released by the FBI on 14 September. Mr Mueller said the bureau was confident that the names and photos were the identities the hijackers had before entering America, even though the identity of four of those have been challenged by people with the same or similar names.
Meanwhile, a document linked to two of the suspected hijackers contains reminders and "rules of engagement" for a strike, a law enforcement source told CNN. The document, written in Arabic and found at the airport in Portland, Maine, where two of the suspected hijackers boarded a flight to Boston, includes the instruction: "Strike your enemy above his neck."
Several pages long, the document also includes rules such as "be very punctual, how to handle yourself at a taxi stand, how to dress", as well as "how to act in certain situations".Reuse content