Recent satellite imagery shows a range of low-level activities at North Korea's main long-range rocket launch site in an indication that Pyongyang may be in the early stages of preparations for a rocket launch, a U.S. research institute said Thursday.

The analysis by the North Korea-monitoring website 38 North followed a series of media reports citing government officials and sources in Japan and the U.S. that the North appears to be making preparations for a long-range rocket launch that could take place as early as in a week.

Commercial satellite imagery taken of the North's Sohae Satellite Launching Station, also known as the "Dongchang-ri" site in the country's northwest, between Dec. 28 and Jan. 25 shows low-level activities at the launch pad, covered railway station, VIP housing area and other places at the site, 38 North said.

Those activities suggest Pyongyang "may be in the early stages of preparation for launching a space launch vehicle," 38 North said. It also said that a launch does not appear imminent, and is unlikely to take place in the coming week.

38 North said, however, that there is a high level of uncertainty about its judgment because the gantry tower work platforms are covered by an environmental cover, which obscures any view of whether a rocket is inside or not. In addition, the movable transfer structure at the site could easily allow for rocket stages to be assembled and transferred to the tower when it's dark or heavily clouded, it said

"If North Korea follows previous pre-launch preparation practices, we would expect to see in the coming days increased site-wide activity, traffic at the fuel/oxidizer storage bunkers, activity at the launch pad and the presence of tracking equipment," 38 North said.

A long-range rocket launch would add to international outrage over the North's Jan. 6 nuclear test. The U.N. Security Council is working on a new set of sanctions on Pyongyang, and the U.S. is also working on unilateral sanctions to punish the regime.

The North's missile program has long been a key security concern in the region and beyond.

The communist nation is believed to have developed advanced ballistic missile technologies through a series of test launches, including the most recent and successful launch in 2012.

That test sparked fears that the North has moved closer to ultimately developing nuclear-tipped missiles that could potentially reach the mainland United States. The country has so far conducted four underground nuclear tests in 2006, 2009, 2013 and this month.

Pyongyang claimed that the latest nuclear test involved a hydrogen bomb, a more sophisticated type of nuclear weapon with much greater yields than ordinary atomic weapons. But the U.S. has cast doubts about the claim, saying initial analysis is not consistent with a thermonuclear explosion. (Yonhap)