North Korea's first spy satellite is "alive" space experts said on Tuesday, after detecting changes in its orbit that suggested Pyongyang was successfully controlling the spacecraft — although its capabilities remain unknown.

After two fiery failures, North Korea successfully launched the Malligyong-1 satellite into orbit in November. Pyongyang's state media claimed it has photographed sensitive military and political sites in South Korea, the United States and elsewhere, but has not released any imagery. Independent radio trackers have not detected signals from the satellite.

"But now we can definitely say the satellite is alive," Marco Langbroek, a satellite expert at Delft University of Technology in the Netherlands, wrote in a blog post.