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 on Saturday. The officials spoke on condition of anonymity because the information is classified as secret.

“Appropriate government agencies are monitoring the situation,” said Gordon Johndroe, a spokesman for the National Security Council. “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 be perhaps shot down by a missile. He said 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 largest uncontrolled re-entry 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 3,175-kilogram science satellite smacked into the Earth’s atmosphere and rained down over the Persian Gulf, a few thousand kilometres from where they first predicted it would plummet.