The US Air Force will launch new satellites today to track those of other countries and counter possible threats to US spacecraft.

Two satellites are due to be sent into high-altitude orbits for the first time.

It is part of a programme that until a few months ago was strictly secret and classified.

The satellites will be launched from Delta IV rockets from Cape Canaveral Air Force Station in Florida.

They will go to the geosynchronous belt, 35,900km above Earth, where crucial US satellites are also orbiting.

Current space surveillance is conducted from Earth or from lower altitudes of a few hundred kilometres above Earth.

The project is known as the Geosynchronous Space Situational Awareness Program, or GSSAP, and was first publicly acknowledged in March.

US Air Force Space Command chief General William Shelton, said the military was now ready to talk about the project.

He said this was partly because officials wanted to send a message to nations plotting to undermine or disable US satellite networks.

Publicising the programme will serve as a "deterrent" and warn adversaries that "you can run but you can't hide," the general said.

Senior officers and intelligence officials are increasingly concerned about space and anti-satellite weapons fielded by China and others that could potentially cripple the communications networks that underpin US military power.

Gen Shelton said the new satellites would bolster the US military's ability to spot adversaries threatening strategic and early-warning satellites in high orbits.

However, he said the US had to start designing future satellites that could survive the more dangerous conditions, and ensure the spacecraft had missile warning mechanisms and more secure communications.