Commercial satellite imagery taken recently showed new activities at a North Korean missile test site where the country tested prototype submarine-launched ballistic missiles through 2016, according to a U.S. institute's analysis released Thursday.

(DigitalGlobe/38 North/Getty/Kyodo)

The imagery of the Sinpo South Shipyard in the eastern region last Saturday suggests a heavy-lift crane was deployed near a missile test stand used between 2014 and 2016 for verification of SLBM launch systems, the U.S.-Korean Institute of Johns Hopkins University said on its North Korea analysis website, 38 North.

A 13-meter-long flatbed truck could also be seen parked nearby, the site said.

"The image, however, is of insufficient resolution to reach a determination as to whether the activity is related to maintenance, removal of the service tower or preparations for an upcoming test," it said.

The latest activities follow Pyongyang's apparently failed test launch on April 16 from the Sinpo area of a ballistic missile which South Korean officials suspect was a medium-range missile.

North Korea had launched what was thought to be a KN-15 in the same region on April 5. The missile flew about 60 kilometers before falling into the Sea of Japan.

Tensions have been growing over North Korea's missile and nuclear program, with the United States having deployed an aircraft carrier and accompanying ships to waters near the Korean Peninsula amid signs Pyongyang is preparing to conduct another nuclear test or carry out an intercontinental ballistic missile test.