Japan, for its part, has said it will shoot the rocket down if it threatens any part of its territory.

South Korean media this week cited unidentified officials as saying that the North had completed installing the three-stage rocket on its launch pad at the Sohae Space Center on the west coast of the country.

But an analysis published Thursday by the U.S. academic website 38 North questions that claim.

Run by the School of Advanced International Studies at John Hopkins University, 38 North says, "We believe these reports are inaccurate based on satellite imagery and lessons from past North Korean rocket launches."

The process may have been delayed by a light snowfall, the website's analysis says, but North Korea could still have the rocket ready in time for the start of the launch window.

This is the first time North Korea has attempted a rocket launch in winter, and experts say the timing of preparations and the launch itself will depend heavily on weather conditions.

"Pyongyang's announcement of a twelve-day launch window, over twice as long as the five-day window for the April 2012 test, may have been based on careful consideration of possible delays or technical problems due to winter weather," 38 North says.

Previous launch attempts by the North in 2006 and 2009 also failed to achieve their stated goal of putting a satellite in orbit and provoked international condemnation.