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A large U.S. spy satellite has lost power and could hit Earth in late February or early March, government officials said Saturday.

The satellite, which no longer can be controlled, could contain hazardous materials, and it is unknown where on the planet it might come down, they said.

The officials spoke on condition of anonymity because the information is classified. It was not clear how long ago the satellite lost power or under what circumstances.

"Appropriate government agencies are monitoring the situation," said Gordon Johndroe, a spokesman for the National Security Council, when asked about the situation after it was disclosed by other officials.

"Numerous satellites over the years have come out of orbit and fallen harmlessly. We are looking at potential options to mitigate any possible damage this satellite may cause."

He would not comment on whether it is possible for the satellite to perhaps be shot down by a missile, saying it would be inappropriate to discuss any specifics at this time.

A senior government official said that lawmakers and other nations are being kept apprised of the situation.

The spacecraft contains hydrazine, a rocket fuel, according to a government official who spoke on condition of anonymity. A colorless liquid with an ammonia-like odor, hydrazine is a toxic chemical that can cause harm to anyone who contacts it.

Uncontrolled reentry of the probe could risk exposure of U.S. secrets, said John Pike, a defense and intelligence expert. Spy satellites typically are disposed of through a controlled reentry into the ocean to render the spacecraft inaccessible, he said.

Pike also said it's not likely the threat from the satellite could be eliminated by shooting it down with a missile, because that would create debris that would then reenter the atmosphere and burn up or hit the ground.

Pike, who is director of the defense research group GlobalSecurity.org, estimated that the spacecraft weighs about 10 tons and is the size of a small bus.

effrey Richelson, a senior fellow with the National Security Archive, said the spacecraft likely is a photo reconnaissance satellite.

Such "eyes in the sky" are used to gather visual information from space about the activities of adversarial governments and terror groups, including construction at suspected nuclear sites or militant training camps.

The satellites also can be used to survey damage from hurricanes, fires, and other natural disasters.

The largest uncontrolled reentry by a NASA spacecraft was Skylab, the 78-ton abandoned space station that fell from orbit in 1979. Its debris dropped harmlessly into the Indian Ocean and across a remote section of western Australia.

In 2000 NASA engineers successfully directed a safe de-orbit of the 17-ton Compton Gamma Ray Observatory, using rockets aboard the satellite to bring it down in a remote part of the Pacific Ocean.

In 2002 officials believe debris from a 7,000-pound (3,175-kilogram) science satellite smacked into Earth's atmosphere and rained down over the Persian Gulf, a few thousand miles from where they first predicted it would plummet.

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