But Mr. Kerry also stressed that the United States was open to negotiations with North Korea if it committed itself to eventual denuclearization.  The Musudan missile has a range of up to 2,500 miles, according to American officials, which means it has the potential to strike targets in Japan, South Korea and even Guam. South Korean officials said earlier this week that North Korea had been making preparations to test the missile.  There has been speculation that Mr. Kim will order the launching to commemorate the anniversary on Monday of the birth of Kim Il-sung, his grandfather and the founder of North Korea, or that it might be fired while Mr. Kerry is in the region.  “If Kim Jong-un decides to launch a missile, whether it is across the Sea of Japan or some other direction, he will be choosing willfully to ignore the entire international community,” Mr. Kerry said at a news conference after meeting with President Park Geun-hye and Foreign Minister Yun Byung-se of South Korea.  “It’s not going to change our current position, which is very, very clear: we will defend our allies,” Mr. Kerry said.  American officials have said that they have not detected efforts by the North Koreans to mobilize forces or make serious war preparations. And Mr. Kerry said the greatest risk would be a conflict that arose out of a series of miscalculations by North Korea, not a deliberate attack. Still, he underscored the risks.  “Kim Jong-un needs to understand, as I think he probably does, what the outcome of the conflict would be,” Mr. Kerry said in a pointed reference to the United States and South Korean military capabilities.  American officials say that the capabilities of North Korea’s Army have begun to erode because of equipment shortfalls and training deficiencies. But it has sought to compensate by fielding a large number of Special Operations forces, producing ballistic missiles and developing chemical arms and nuclear weapons, officials say.  While the United States and South Korea have publicly said a launching would be a serious provocation, some American officials say it might also serve as a way for Mr. Kim to back away from a confrontation while saving face.  “That might give Kim Jong-un some sort of off ramp,” said an American official who, following diplomatic protocol, spoke to reporters on the condition of anonymity. “You could say, ‘I have stood up to the United States; I launched a missile.’ ”  The American official said the United States had not seen any indications that a launching was imminent but noted that it could be carried out with little or no notice.  Mr. Kerry is wrapping up a six-nation tour. With tensions running high on the Korean Peninsula, Mr. Kerry arrived in Seoul, the South Korean capital, on Friday to reassure America’s ally and discuss United States-South Korea issues before Ms. Park comes to Washington next month to meet with President Obama.  Though he has traveled to Asia for more than four decades, Mr. Kerry was visiting South Korea for the first time. Mr. Kerry noted that Mr. Obama had canceled some American military exercises to contain tensions in the region.  Mr. Kerry also dispensed with one of the rituals of many visiting American dignitaries: a high-profile trip to the demilitarized zone between the North and the South.  Besides stops in South Korea and Japan, Mr. Kerry will also visit China on Saturday to urge officials there to persuade North Korea to abandon its nuclear weapons program.  Reiterating the longstanding American position, Mr. Kerry said the United States would never accept North Korea as a nuclear state. Talks involving the United States and North Korea, he said, can take place only if Mr. Kim agreed to move to denuclearization.  “They simply have to be prepared to live up to their international obligations and standards, which they have accepted, and make it clear they will move to denuclearization as part of the talks, and those talks can begin,” Mr. Kerry said. “But they have to be really serious.”  At the same time, a joint statement issued by Mr. Kerry and Mr. Yun endorsed Ms. Park’s efforts to establish a dialogue with North Korea.  Under the previous South Korean leader, Lee Myung-bak, Washington and South Korea moved in lock step, keeping contacts with the North to a minimum and insisting on applying sanctions until North Korea would make serious steps toward denuclearization.  Under Ms. Park, South Korea appears to have eased the stance. While South Korean officials said they wanted dialogue with North Korea to help explore ways of defusing the current crisis, they insisted they had no intention of compromising on the fundamental question of its nuclear program.  “We will strongly retaliate against North Korean provocations, but if North Korea accepts change and joins us in dialogue, we will try to build mutual trust for co-prosperity,” Ms. Park told Mr. Kerry, according to an account provided by her office.  As part of the trust-building effort, the South Korean government supported the provision of medicine to North Korea by nongovernmental groups. “Truly humanitarian aid and transparent aid,” Mr. Yun said, “is totally acceptable.”  The disclosure on Thursday that the Defense Intelligence Agency had determined with “moderate confidence” that North Korea was capable of making a nuclear weapon small enough to be delivered by a ballistic missile was the subject of much attention here.  Mr. Kerry said the United States did not believe that the North Koreans had such a “fully tested and available capability.”  “Obviously, they have conducted a nuclear test, so there’s some kind of device,” Mr. Kerry added. “That is very different from miniaturization and delivery. Does it get you closer to the line that is more dangerous? Yes.”
Secretary of State John Kerry warned North Korea not to test-fire its Musudan missile and said the nation would lose if a conflict broke out.