Bin Laden's plan was to strike before September 11

Osama Bin Laden wanted to launch his attacks on New York and Washington months before 11 September 2001, but postponed the plan because the hijackers were not ready, investigators have concluded.

Osama Bin Laden wanted to launch his attacks on New York and Washington months before 11 September 2001, but postponed the plan because the hijackers were not ready, investigators have concluded.

The independent panel on the attacks has uncovered evidence that Bin Laden originally intended the strikes in May or June of that year. He agreed to the delay after Mohamed Atta, the senior hijacker, told him his team members were not yet ready.

The finding is in a draft report likely to released when the commission meets tomorrow for its final public sessions before presenting its overall findings. Law enforcement investigators had believed al-Qa'ida may have brought forward its plan after the arrest of Zacarias Moussaoui, accused by some of being the intended 20th hijacker, but not that it delayed it.

The Washington Post reported yesterday that the panel's conclusions were based at least partly on information from the interrogation of Khalid Sheikh Mohammed, an alleged senior al-Qa'ida operative in US custody. Mr Mohammed is accused of being the mastermind of the attacks and it appears he may have persuaded Bin Laden to delay the assault.

"[The report is based on] intelligence coming in that they wanted an earlier date," said one official, who has seen the draft report. "It's something really new." Though this is the first evidence of a delay, investigators have long thought the hijackers were flexible about their timing.

Analysts who have pored over the hijackers' computer and e-mail records believe they carefully researched flight plans and schedules, and specifically selected Boeing 757 and 767 jets, on which they had trained. This was more important than the choice of a particular airport. The claim that 11 September 2001 was not a date al-Qa'ida had fixed in stone will add to the debate that has swirled about the potential symbolism of the day.

Some have speculated that the date was deliberately chosen to represent 911, the emergency telephone number used in the US. Others have suggested the date marks the day in 1922 that Britain took charge of Palestine under a League of Nations mandate. Other, more cryptic deconstructions, claim the date somehow relates to the number of people on board the two planes flown into the World Trade Centre towers.

Family members of those who died in the attacks said news that the hijackers might have chosen a different date was shocking, raising as it does the possibility that the hijacked planes would have contained different passengers and the twin towers may have populated by different people.

"This is an example of al-Qa'ida postponing something and carrying it through with great success," said Kristen Breitweiser, who husband died in the towers. "This means they can follow through, and we have to learn from that."

Tomorrow the commission is expected to release another report addressing the question of whether US fighter jets may have been able to intercept and shoot down American Airlines Flight 77, which the hijackers flew into the Pentagon. There has been persistent controversy about why the fighters were not scrambled earlier and whether they had been given the authority to shoot down the passenger plane. The commission's final report is expected in late July.

* Vice-President Dick Cheney has repeated that Saddam Hussein had "long-established ties" with al-Qa'ida, a claim challenged by some policy experts and lawmakers.