A US research institute said on Wednesday that a report run by a North Korean monitoring website by Johns Hopkins University's School of Advanced International Studies in Washington cited the visuals revealed North Korea is opening a new tunnel for nuclear testing on North Korea's east coast where three previous nuclear tests were run.
The report said the photos from the satellite showed digging of a new tunnel besides three others where North Korea has either carry nuclear tests or excavated tunnels in the past.
It also said, "While there are no indications that a nuclear test is imminent, the new tunnel adds to North Korea's ability to conduct additional detonations at Punggye-ri over the coming years if it chooses to do so."
South Korea's local media quoted a South Korean government source on October 30 as saying workers and vehicles were active on the site working for a tunnel, which showed an intention of conducting of a nuclear test although this did not seem to be forthcoming.
South Korean Unification Ministry spokesman Jeong Joon-hee rejected to approve the report but added that the country and the United States are closely watching for any nuclear activity by the North.
The report comes as the leaders of South Korea, Japan and China are due to meet in Seoul on Sunday where North's pursuit of weapons of mass destruction is likely to be negotiated.
North Korea has been regularly working on its nuclear programme, but a fourth nuclear test was not seen as imminent, particularly after it came to a deal with South Korea in August to work towards relieving tensions on the peninsula and improve ties.
North Korea which is under United Nations sanctions that forbid commerce that can fund its arms program has conducted three nuclear tests so far, the last of which was in 2013.
It was condemned by the international community, including its premier diplomatic ally China for its last move.
The United States and South Korean defense chiefs expressed "grave concern" over North Korea’s nuclear test plans and pushed it to quit all activities under its nuclear program as soon as possible.