North Korea is expected to complete the expansion of a long-range rocket launch site on the country's west coast by this fall, a report said Thursday, in a move that will allow the regime to fire bigger rockets with heavier payloads.

The website 38 North, run by the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies, made the assessment based on recent satellite imagery of what the North calls the Sohae Satellite Launching Station, according to an Associated Press report.

In December 2012, the North succeeded in putting a satellite into orbit on a long-range rocket fired from the launch pad in a surprise move that demonstrated to the world that it has moved closer to developing a nuclear missile that can reach the U.S. mainland.

Pyongyang has been working to upgrade the launch site to make it handle bigger rockets.

According to the report, the North has worked rapidly to expand the launch tower and has progressed on a railway to access it. It also has completed external work on two prominent, domed buildings at the site, whose function is uncertain.

Thursday's assessment contrasts the think tank's own analysis made just a few weeks ago. In a July 30 report, 38 North had said that modifications could be completed by 2015. (Yonhap)