The crash came shortly after two other hijacked airlines were flown into the twin towers at the World Trade Center in New York.

Judicial Watch filed the freedom of information request in 2004, but the Pentagon refused to release the video because it was part of the investigation involving al-Qaeda plotter Zacarias Moussaoui, the group said.

This February the group sued the government over its refusal, saying there was "no legal basis" for it.

Washington agreed to release the video after a court sentenced Moussaoui to life in jail for his role in 9/11 earlier this month, a Judicial Watch spokeswoman told the BBC.

The group said it fought to obtain the video because "it was very important to complete the public record" on the attacks.

French author Thierry Meyssan alleged that Flight 77 did not crash into the Pentagon and suggested a truck bomb or missile caused the damage.

Such views are challenged by witness testimony at the scene of an aircraft fitting the description of Flight 77 crashing into the site.

Correspondents say the release of the video is not unhelpful to the Bush administration.

The footage serves as a graphic reminder of why the US launched its global war on terror and is still fighting it, the BBC's Adam Brookes in Washington says.