Updated

A U.S. research institute says an upgrade of North Korea's main rocket launch pad could be complete by April, meaning it would be ready for new launches.

The U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies says new satellite imagery shows modifications underway at the west coast Sohae site mean it could eventually accommodate rockets 50 meters long. North Korea is not thought to have such a large rocket, but in December 2012 it launched into space the 30-meter-long Unha-3. The U.S. viewed that as a worrying sign of the North's development of ballistic missile technology.

The new analysis was published Thursday on the Johns Hopkins institute's website, 38 North, which reports no sign of launch preparations as of late January. Launch preparations can take about six weeks.