Russia launched an unmanned Soyuz U rocket from Plesetsk Cosmodrome on Tuesday carrying a classified military spacecraft believed to be an imaging spy satellite.

Liftoff occurred at 1755 GMT (1:55 p.m. EDT) and orbit was achieved successfully for the Cosmos 2377 spacecraft.

Russian space experts suggest the satellite could be a Yantar or Kobalt imaging spacecraft.

The launch marked the 1,659th successful flight of a Soyuz rocket. It was the fifth Soyuz mission of the year, and extended to 63 the consecutive string of successful Soyuz launches.