“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.”

It is suspected that the craft in question could be USA 193, a radar satellite that malfunctioned shortly after it was launched in December 2006.

Possible hazards from the satellite include beryllium, a toxic metal commonly used in the defence and aerospace industries.

Due to onboard malfunctions, the craft may also be carrying a large amount of hydrazine propellant.

Hydrazine can damage the central nervous system and is fatal in large doses.

But space scientists are downplaying the hazards posed by debris from the satellite reaching the ground.

"When they re-enter they usually burn up in the atmosphere because a lot of heat has developed and there is a lot of friction," said Dr Ruediger Jehn, a space debris analyst at the European Space Agency.

"Only heat-resistant or very heavy objects will survive."

"There is a risk in this case that something will hit the ground, but given that the Earth is so big, the probability in this case that someone will be hit is really remote."