He said: "Based on our analysis of satellite imagery, we judge that there is a hollow space, which measures about 60 to 100 metres, at the bottom of Mount Mantap in the Punggye-ri site".
The incident is believed to have happened on October 10, but another news agency, South Korea's Yonhap, said it was still unclear when the disaster took place. Kim Jong Un made similar statements in September, calling the president "deranged" in a statement to circulated on KCNA.
According to the Asahi newspaper report, a computer simulation of possible leaks of radioactive materials ran by the Korea Institute of Ocean Science and Technology (KIOST) showed that meteorological conditions at the time of North Korea's nuclear test would have allowed for radioactive materials to carry into the atmosphere in a northeastern direction.
Defense Secretary James N. Mattis, Secretary of State Rex Tillerson and Vice President Mike Pence have all visited the DMZ, a 2.5-mile wide strip of land that has separated the two countries since 1953.
"Chairman Kim has recently strengthened the monitoring of his senior officials and resumed the purge and executions that he had refrained from for some time", the agency said. Their relationship was forged in the bloodshed of the Korean War, when Mao Zedong sent millions of "volunteers" to fight US-led United Nations forces to a standstill.
Trump will meet for the first time with Philippine President Rodrigo Duterte, who has been accused of human rights abuses, including killing suspected drug dealers.
The launch of a Hwasong-12 missile on September 16, 2017.More news: Playboy Halts Brett Ratner's Hugh Hefner Biopic Following Allegations
The official, speaking on customary condition of anonymity in briefing reporters, noted the two Trump administration forays to the zone.
One indirect tool at Trump's disposal, U.S. officials told Reuters, is the threat of imposing further economic sanctions on North Korea. Trump is playing golf with Abe during the trip, according to White House officials. The South Koreans are looking "to better develop their squad leaders and platoon sergeants to operate effectively at the decentralized level and operate off of commanders' intent and apply discipline initiative to get after combat, if they have to", he said. Since taking office Trump has already withdrawn the U.S. from the Trans-Pacific Partnership and the Paris Agreement on climate change.
"In the case of a heated tensions on the Korean peninsula, especially in the face of the repeated provocations from North Korea, I hope that state leaders of countries relevant to the Korean peninsula could reach constructive deals, and such deals are expected to help to prevent North Korea from its provocations and [force the North to] return to talks", Noh said.
"Trump will probably tell the Chinese president, "'I'm coming after you on trade, '" Christopher Johnson, a China analyst at the Center for Strategic and International Studies, told the Washington Times. He cautions Trump against "any kind of tweeting" that would criticize the leader of a country he's visiting.
"The Chinese appreciate precision when it comes to formal diplomatic engagements", said Selfridge.
Given the storms facing Trump domestically - from tax reform to this week's indictment of his former advisers Paul Manafort and George Papadopoulos - Schell said that Trump is "leaving America at a very difficult time". They are a learning Army, he said, and have learned from the incident where the infiltrators came in.