A January 2001 French secret services report that revealed al-Qaeda was planning to hijack an aircraft was given to a CIA agent, according to the French newspaper Le Monde.
The newspaper says it has obtained 328 pages of classified documents that show foreign agents infiltrated al-Qaeda's network.
It produced nine reports between September 2000 and August 2001, including the January 2001 document called 'Plan to hijack an aircraft by Islamic radicals'.
It says the operation was discussed in Kabul at the start of 2000 by al-Qaeda, Taliban and Chechen militants.
The hijack was meant to happen between March and September 2000 but the organisers delayed the plan 'because of differences of opinion, particularly over the date, objective and participants,' Le Monde said, citing the report.
Attacks on New York and Washington DC eventually took place on 11 September 2001 and killed almost 3,000 people.
Le Monde said the January 2001 report was handed over to a CIA operative in Paris, but that no mention of it was made in the official US September 11 Commission which produced its findings in July 2004.
Le Monde said the documents also show the French believed al-Qaeda leader Osama bin Laden was still receiving help from family members and senior officials in Saudi Arabia in advance of the 11 September attacks.
This was despite attempts to clamp down on the network after al-Qaeda's attacks on US embassies in Tanzania and Kenya in 1998.
