Passengers of United Airlines Flight 93 put up a stiff resistance leading to a September 11 hijacker to instruct the terrorist-pilot to crash the plane into a Pennsylvania field, a testimony by FBI director Robert Mueller, which was recently disclosed, shows.

ABCnews said the disclosure puts paid to the theory that insurgent passengers grappled with the terrorists inside the cockpit leading to the crash.

Mueller's testimony, according to the ABCnews report, was based on government's analysis of cockpit recordings.

The findings are part of the July 24 congressional report on September 11 attacks.

The FBI, however, has been at pains to explain that its findings do not diminish the heroism of the passengers who tried to overpower the hijackers.

In phone calls from the plane, four passengers said they and others decided to fight the hijackers after learning of the attacks on the World Trade Centre in New York that morning.

"While no one will ever know exactly what transpired in the final minutes of Flight 93, every shred of evidence indicates this plane crashed because of the heroic actions of the passengers," FBI spokeswoman Susan Whitson said Thursday.

Thirty-three passengers, seven crew members and the four hijackers died when Flight 93 crashed, one of four hijackings that killed more than 3,000 people on Sept 11.