The mysterious probe had lurked in Earth's orbit for more than half a decade and was reportedly designed to inspect and destroy enemy satellites in orbit.

It broke up in orbit unannounced in late December, according to one ex-Nasa expert.

"In Dec 2013 Russa launched ... three military communications satellites and a fourth, initially unannounced, payload, later acknowledged with the cover name Kosmos-2491," astronomer Dr Jonathan McDowell wrote on Twitter.

"It appeared to end its mission in 2014. However, at about 1321 UTC on 2019 Dec 23, the satellite made an orbit change and 10 debris objects have now been catalogued."

The sudden appearance of debris suggests the spacecraft broke apart in orbit. The Kremlin has not commented on the loss of the satellite.