Japan's Kyodo News reported Sunday on new satellite imagery showing the installation of a cover over the launch pad at the Sohae Satellite Launching Station in Tongchang-ri Cholsan County.
U.S. intelligence agencies say the details are unclear, but expect the installation to be completed this month.
The development is especially concerning, as covers were placed on the side and other parts of the launch pad in the final stages of North Korea's preparations for two separate long-range rocket launches in 2012.
South Korea reported last month that North Korea had completed an upgrade to the launch pad that would allow it to fire a long-range missile twice the size of the rocket launched in 2012.
There is speculation the preparations could be for a possible launch in October to mark the 70th anniversary of the founding of the North's ruling Workers' Party.
The move would be sure to further isolate the regime from the international community, though there are signs it may already be taking steps in that direction.
Pyongyang on Sunday notified the France-based organizer of an international military sports event to be held in Seoul in October that it will not attend.
Seoul's defense ministry says the North gave no reason for its decision.
The North also recently rejected the South's invitation to an international security dialogue set to take place in Seoul next month.
Connie Kim, Arirang News.