The North has conducted all its three nuclear tests at the Punggye-ri site in the northeastern part of North Korea.
Seoul:
US experts said Saturday that recent satellite photos showed no sign of North Korea preparing a new nuclear test, contrary to reports in the South Korean media.
Satellite imagery from September 27 and October 25 of the Punggye-ri nuclear test site indicate "no signs that the North is excavating a new tunnel", the US-Korea Institute at Johns Hopkins Univesity said on its closely-watched website, 38North.
The main observable activity is the construction of a new building at the Main Support Area, it said.
Activity at both the west and south portals of the site has been at a low level, an indication that the North continues to focus largely on tunnel maintenance, it added.
The North has conducted all its three nuclear tests -- in 2006, 2009 and 2013 -- at the Punggye-ri site in the northeastern part of North Korea.
South Korea's Yonhap news agency, quoting an unidentified government source, said the North was believed to be digging a new tunnel there in what could be a sign that the Stalinist state is preparing for its fourth nuclear test.
Fears had grown that the country might carry out a fresh nuclear test to mark the 70th anniversary of the founding of North Korea's ruling Workers' Party on October 10 but none was carried out.