A Washington-based research organization said North Korea has completed a major upgrade of its main rocket launch site.
The U.S.-Korea Institute said the overhaul of the Sohae Satellite Launch Station is likely meant to accommodate larger rockets.
The findings were based on commercial satellite photos and published on the institute's popular 38 North website.
The report says there is no evidence of an imminent rocket launch, but warns that one could occur by the end of the year.
Pyongyang received international condemnation in 2012 after sending a satellite into orbit using a Unha-3 space launch vehicle.
The institute said the North is believed to be developing a much larger rocket, but could be at least several years away from completion.
Until the larger rocket is operational, the research group said North Korea could launch another Unha rocket from the Sohae facility.
North Korea regularly threatens nuclear war against South Korea, Japan and the U.S., but insists its rocket program is peaceful.
The isolated, communist government is banned under United Nations sanctions from conducting ballistic missile and nuclear tests.