The US government has said one of its spy satellites has gone out of control and is expected to crash to Earth some time late next month or in March.
Officials said the satellite, which is the size of a small bus, had lost power and propulsion, and could contain hazardous materials.
The White House said it was keeping other countries abreast of the satellite's course.
A National Security Council spokesman said numerous satellites had come out of orbit over the years and fallen harmlessly.
'We are looking at potential options to mitigate any possible damage this satellite may cause', he said.
In recent years, Nasa has safely brought defunct satellites back to Earth.
In 2000, the space agency manoeuvred the Compton Gamma Ray Observatory to a splashdown in the Pacific Ocean.