The North has threatened to turn the capital of South Korea into "a sea of fire" and to launch nuclear weapons at the USA.

Secretary of State John Kerry 's insistence Friday that the United States "would not accept" a North Korea with nuclear weapons laid out no new policy on how to stop it from happening.
The long-standing U.S. demand that the North cease its nuclear activity predates the Obama administration and is no closer to being adhered to than it was two decades ago, analysts say.
Actions he did announce, such as President Obama's scaling back of military exercises with U.S. ally South Korea in the face of North Korean threats, are likely to embolden North Korea, says Bruce Klingner, a former director of the CIA's Korea Desk who's at the Heritage Foundation.
"With North Korea taking several steps forward and you take a step back, it only confirms in their mind that the United States will back down," Klingner said.
Kerry is on his first stop of a four-day visit to Asia, which is to include stops in China, the North's greatest ally, and Japan. It comes as the North's dictatorial regime led by Kim Jong Un, 30, prepared to celebrate the birthday of his grandfather, Kim Il Song, founder of the North Korean state.
The North has threatened to turn the capital of South Korea into "a sea of fire" and to launch nuclear weapons at the USA. The North does have nuclear weapons technology and has fired long-range missiles in tests.
This week, North Korea moved a missile into position that is capable of reaching U.S. forces in Guam. Japan's Kyodo news agency cited a Japanese defense official saying the North Korean Masudan missile launcher was seen in an upright position near the North Korean east coast.
The United States has said the North cannot reach the continental USA but is getting closer to producing an intercontinental missile capable of reaching the U.S. homeland.
Kerry said, "We will defend our allies," South Korea and Japan, "and we will defend ourselves."
He said President Obama had ordered several military exercises "not be undertaken," and "we have lowered our rhetoric significantly" in an effort to "find a way for reasonableness to prevail here."
Klingner says that kind of talk is counterproductive.
"North Korea will look back at its history and see that any time it attacked, the United States and South Korea tended to back down," he said. "In the past, by not responding militarily to North Korean attacks, the United States and South Korea usually tried to get back to negotiations or offered benefits to reduce tensions that North Korea has raised."
John Bolton, who served as the U.S. ambassador to the United Nations under President George W. Bush, says the only way to prevent North Korea from getting nuclear weapons it can use to threaten and blackmail the region is for the United States to work with China to bring about the collapse of the North Korean regime and reunification of the two Koreas.
China, which provides North Korea 90% of its fuel and much of its food and is its only ally except for Iran, has viewed North Korea as a useful buffer separating U.S. troops from the Chinese border.
It fears a collapse of the North Korean state would cause a flood of millions of hungry refugees into China. Yet recent articles in Chinese government-controlled media and think-tank publications have raised the idea of cutting off aid to North Korea, Bolton said.
U.S. diplomats should work with China to reassure it on security, promise aid for refugees and encourage civilians to stay in North Korea, Bolton said. It's in China's interests for the North Korean regime to collapse, he said.
"The difference now is a nuclear North Korea really does cause a problem for China," he said. "It's said for years it doesn't want a nuclear North Korea because it causes instability on the peninsula and economic disruption in Northeast Asia. They're right. North Korea is ready to test a missile which the U.S. Defense Intelligence Agency thinks is capable of carrying a nuclear warhead."
Klingner said the United States should respond to the threats with a pledge to protect its allies and an expansion of more comprehensive sanctions to further damage and isolate the North Korean regime.
Lawmakers in South Korea and Japan are increasingly expressing an interest in developing their own nuclear defenses.
China does not want that, Bolton said. Once the North has nuclear weapons of its own, China's other neighbors may have no choice but to go nuclear, and the North will probably behave even worse.
North Korea has been "lashing out," without nukes, Bolton said. "Do you think they'll be better behaved with nuclear weapons?"
In Seoul, Kerry said calming the situation is his first priority.
"The greatest danger here, we all agree, is for a mistake," he said. "The greatest danger is that something happens and there's a response to that something, and then things somehow inadvertently were to get out of control. "
He called on Kim Jong Un "to recognize that this is a moment for responsible leadership, and it's a moment to try to reach for the good possibilities, not try to guarantee the bad ones."