WASHINGTON — The Pentagon has concluded that a missile destroyed a crippled spy satellite's fuel tank last Thursday and that the rocket fuel has dissipated.

Pentagon officials said Monday that they based their conclusion on various measures, including video shot from the missile warhead as it approached the satellite. Officials did not, however, release that video.

Military officials decided to try to down the satellite, which failed within hours of its December 2006 launch and was returning to Earth, because it was carrying 1,000 pounds of hydrazine. Officials feared the satellite and its toxins could land in a populated area.

"From the debris analysis, we have a high degree of confidence the satellite's fuel tank was destroyed and the hydrazine has been dissipated," Marine Gen. James Cartwright, the vice chairman of the Joint Chiefs of Staff, said in a statement released Monday.

Within hours of launching an SM-3 missile from the USS Lake Erie on Thursday, Pentagon officials were optimistic they had struck the satellite. Video images of the missile striking the satellite showed a fireball, followed by a large vapor cloud, which scientists believe was the hydrazine evaporating.

It was the first time the military used tactical missiles to shoot down a satellite. The USS Erie, an Aegis class missile cruiser, was stationed roughly 600 miles west of Hawaii.

The military now is monitoring roughly 3,000 pieces of satellite debris re-entering the Earth's atmosphere at a space operations center at Vandenberg Air Force Base in California. None of the pieces is larger than a football, the military said. Most, if not all, are unlikely to reach the Earth's surface.

The spy satellite was built on behalf of the National Reconnaissance Office. The operation to shoot it down cost roughly $40 million.

ON THE WEB

Video: See the missile strike the satellite.

Read about the controversy surrounding the shoot-down.