Tensions are high on the Korean Peninsula following an artillery exchange Tuesday between the two sides that left two South Korean marines dead. It was one of the most dramatic confrontations between the two sides since the Korean War ended in 1953. And it comes on the heels of a trip to North Korea by a team of top nuclear scientists, including Siegfried Hecker, the former director of Los Alamos National Laboratory. Hecker says North Korea is working on two new nuclear facilities, a water power reactor and a uranium enrichment plant. The latter is significant because it could produce enough highly enriched uranium to make a nuclear weapon.
North Korea on Tuesday shelled a populated border island held by the South and South Korean forces promptly returned fire. The exchange forced the island's 1,600 residents to flee to shelters.
"I was lying down and watching television and I heard the bang bang sound," said a woman. "I thought that I would die."
North Korea watchers in the West are transfixed, especially following reports by top U.S. scientists that North Korea's nuclear capacity has advanced quickly since Western experts were last allowed in.
Siegfried Hecker is the former director of Los Alamos National Laboratory, the top U.S. national security research institute. He described his reaction at seeing 2,000 working centrifuges at a sophisticated uranium enrichment facility.
"My jaw just dropped," said Hecker. "I was stunned to see what looked like hundreds and hundreds of centrifuges lined up two each ... it was just stunning in a clean facility, modern facility. Looking down I said, 'Oh my God, they did what they said they were going to do.'"
Hecker was not allowed to take pictures of the site, which he said is far from producing a bomb.
"To get from what I saw to a hydrogen bomb that's just an incredible step," he said.
But he did suggest that North Korea has gotten help over the years in acquiring nuclear skills, perhaps from agents in Pakistan. And that a sophisticated procurement process has allowed North Korea to skirt sanctions, with even Germany and Russia shipping aluminum that could be used in plant construction.
North Korea analyst Marcus Noland says sanctions against North Korea have had limited effect.
"The problem with sanctions is that North Korea's largest trading partner is China, and China has shown absolutely no interest in implementing sanctions," said Noland.
Hecker and his team say Chinese scientists are surprised at the pace of North Korea's nuclear development.
North Korean analyst Victor Cha says the U.S. will need China on its side if it wants to get back to the nuclear weapons bargaining table with North Korea.
"It's what one person once described to me as the land of lousy options," said Cha. "You are never choosing between good and bad options. You are choosing between bad, worse and the worst."
Marcus Noland says it could be as simple as this:
"They want to convince us that they are a nuclear power and despite agreements they have signed in the past, they have no real interest in denuclearization," he said. "And we should simply get used to it."