Seoul, Sha'ban 17, 1434, Jun 26, 2013, SPA -- Satellite photos show fresh construction activity at an underground North Korean nuclear test site, a US research institute said Wednesday, but the imagery does not appear to show Pyongyang preparing for an imminent nuclear detonation, dpa reported. The images reveal tunnel work being done at the Punggye-ri test site in the north-east of the country, announced the US-Korea Institute at Johns Hopkins University. Researchers said the construction began in late April and has since picked up momentum. While it does not signal new nuclear tests in the short-term, the tunneling may be laying the groundwork for such activity in the future, the institute said. Punggye-ri was the likely site of the Pyongyang's third nuclear test on February 12. --SPA 21:38 LOCAL TIME 18:38 GMT www.spa.gov.sa/1124248