Japan's top government spokesman has called a North Korean threat to sink Japan with a nuclear bomb extremely provocative and outrageous. That didn't work. North Korea withdrew from the treaty and continued its nuclear pursuit.
"I agree that the South needs to bolster its defense capabilities against the North's advancing nuclear and missile programs", Moon said in an interview with CNN.
North Korea's announcement came just hours after a large quake was detected near the country's only known nuclear test site in the mountainous region of North Hamgyong province.
North Korean leader Kim Jong Un provides guidance with Ri Hong Sop (3rd L) and Hong Sung Mu (L) on a nuclear weapons program in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang September 3, 2017.
While it was impossible to put a number on the scale of the North Korea risk, war games carried out through history have simulated what could happen as a result, said Tina Fordham, managing director and chief global analyst at Citi.
According to the statement, both leaders agreed to work together to deal with the current serious situation and called on the worldwide community to rigorously and fully implement relevant UN Security Council resolutions to maximise pressure on North Korea.More news: Diplomacy takes unusual twist in Shinzo Abe and Narendra Modi's roadshow
"Prime Minister Modi and I are in full agreement on this", he said.
Moon said just because the United States and South Korea were now pursuing a firm path of sanctions and military drills, the time for negotiations wasn't over.
The United Nations Security Council approved fresh sanctions against Pyongyang in a unanimous vote on Monday, slashing the cap on crude and refined oil exports to the country by 30 percent.
"To respond to North Korea by having our own nuclear weapons will not maintain peace on the Korean Peninsula and could lead to a nuclear arms race in northeast Asia", Moon said.
Writing for 38 North, the Johns Hopkins University website dedicated to North Korea issues, analysts Frank V. Pabian, Joseph S. Bermudez Jr. and Jack Liu say North Korea's site now has "additional slippage" in "pre-existing landslide scars" and a "possible subsidence crater". "It's a very reckless choice made by North Korea that is not helpful to North Korea itself or inter-Korean relations and threatens world peace". But the data were not sufficient to determine what type of nuclear device the North had detonated, it said.