Activity continues to be detected at North Korea's western satellite launching ground with preparations seemingly under way for the second attempt to launch its first military spy satellite.

Citing satellite imagery of the Sohae Satellite Launching Station from Saturday, Voice of America(VOA) said a mobile structure used to erect a space launch vehicle has been relocated to the center of the launch pad.

The movement was detected at the North's previous launch facility, some three kilometers away from a new site where its failed rocket firing took place last week.

VOA said, however, that it remains uncertain whether the launch vehicle is inside the mobile structure or why it was relocated.

While similar activity had been spotted prior to the first launch last Wednesday, there is speculation that the second attempt may be carried out at the old launching ground.