MOSCOW (Reuters) - One of two Russian defense satellites launched on Dec. 5 did not separate from the Soyuz carrier rocket’s upper stage and is considered lost, Russian news agencies reported.

A Soyuz-2.1B rocket carrying two satellites was launched from the Plesetsk cosmodrome in the Russian north-western Arkhangelsk region, with the Defence Ministry saying on its web site on Dec. 5 that the launch was successful.

But TASS news agency cited an unnamed source saying on Monday that the Kanopus-ST satellite “was considered lost” after it failed to separate due to a malfunction of one of the four locks holding the satellite.

This was the second launch of the Soyuz-2.1B three-stage carrier rocket that is used for placing payloads into low Earth orbit. The first launch took place in late December 2013, the ministry said in its statement.

On Dec. 11, American, Russian and Japanese astronauts are expected to return to Earth from the International Space Station(ISS) aboard a Russian Soyuz capsule.

The Defence Ministry was not immediately available to comment.