The US website also confirmed that the North Portal, where five of the six North Korean nuclear tests were carried out, has remained in a dormant state. However, stepped-up tunnelling activities have been detected at the nuclear test site's West Portal.
Elsewhere at the site there was unusual activity with some 100-120 personnel lined up in formation in the courtyard, their objective unknown.
The report is based on an analysis of new commercial satellite images of the nuclear site by Frank Pabian and two other nuclear experts.
"These activities underscore North Korea's continued efforts to maintain the Punggye-ri site's potential for future nuclear testing", 38North concluded. "It appears that the spoil pile has been expanded significantly along its south side".
In another article on 38North, Alexander Vorontsov, the head of the Institute of Oriental Studies of the Russia Academy of Sciences, was quoted as saying that North Korean diplomats were extremely serious about the possibility of war between North Korea and the U.S.More news: Chelsea Manning is running for Maryland's Senate
President Trump, who has repeatedly called Kim Jong-Un "Rocket Man" and his government a "band of criminals" while threatening to destroy the country with "fire and fury", said Thursday that he has a "very good relationship" with the Korean dictator.
The president told The Wall Street Journal "I probably have a very good relationship with Kim Jong-un", adding "I have relationships with people".
"I have relationships with people".
"You'll see that a lot with me", he said. However, he did not reveal if he had actually spoken to Kim. "I'm not saying I have or haven't", he said.
But Pyongyang - which boycotted the 1988 Summer Olympics in Seoul - agreed Tuesday to send athletes and officials to the Games as the North and South held their first formal talks in two years at Panmunjom in the Demilitarised Zone.