North Korea has been confirmed to be carrying out excavation work at its Punggye-ri nuclear test site, raising speculation that the regime is preparing for a new nuclear test.
 
A South Korean military official said Friday that military intelligence assets had verified ongoing tunnel construction at the site.
 
The official said although it appears the North intends to conduct a nuclear test in the tunnel, whether a test is imminent needs to be determined through additional analysis.
 
The North has conducted three nuclear tests at the site so far, in 2006, 2009 and 2013.