Seoul , South Korea ( CNN ) -- Secretary of State John Kerry said Friday that the United States is prepared to enter into talks with North Korea , but only if it is serious about negotiating the denuclearization of the Korean Peninsula . Kerry is in Seoul meeting with South Korean Foreign Minister Yun Byung-se amid heightened tensions spurred by North Korea 's recent nuclear threats and provocations . He landed in Seoul , about 30 miles from the demilitarized zone separating the two countries . The Korean peninsula is rife with tensions over the belligerent threats issued by Pyongyang . The United States will defend itself and its allies if needed , Kerry said . `` North Korea will not be accepted as a nuclear power , '' he said at a news conference with Yun . `` The rhetoric that we are hearing is simply unacceptable . '' Pentagon intelligence assessment suggesting North Korea may have the ability to deliver a nuclear weapon on a missile has set off a flurry in Washington , with top officials trying to play down concerns about the capabilities of the Pyongyang regime . The Pentagon 's intelligence arm has assessed with `` moderate confidence '' that North Korea has the ability to deliver a nuclear weapon with a ballistic missile , though the reliability is believed to be `` low . '' First disclosed by a congressman at a hearing Thursday and then confirmed to CNN by the Defense Department , the assessment by the Defense Intelligence Agency is the clearest acknowledgment yet by the United States about potential advances in North Korea 's nuclear program . Will Kim Jong Un listen to China ? The United States calculates that a test launch of mobile ballistic missiles could come at any time . But a senior administration official said there is no indication that missiles that North Korea is believed to be readying for tests have been armed with any nuclear material . The surprising development comes amid heightened tensions on the Korean Peninsula . North Korea has unleashed a torrent of dramatic threats against the United States and South Korea in recent weeks , including that of a possible nuclear strike . Kerry 's Asia trip will include visits to China and Japan . The tour comes at a time when all three countries have new leaders . The North Korea we rearely see . It 's the first time the Obama administration is engaging with all three countries in the same trip , the State Department said . The top U.S. diplomat 's trip comes days after he warned the North on what he calls leader Kim Jong Un 's `` provocative ... dangerous , reckless '' rhetoric and actions . China , U.S. officials say , is growing more concerned about the North 's provocations , but it also is closely watching Washington 's latest military moves in the region . Report sparks intel controversy . Kerry will try to convince leaders in Beijing that Pyongyang is `` putting China 's own interests at risk , '' a senior administration official said . Pyongyang 's provocations are the immediate threat , but the Obama administration 's `` pivot to Asia '' has broader strategic implications for Beijing . Throughout his Asia swing , Kerry will have to balance his short-term and long-term diplomatic objectives . `` Secretary Kerry can reassure regional states that , as a Pacific century dawns , the United States will continue to be right in the middle of it and will not allow any power to edge the United States out of a region where nearly every country welcomes its leadership , '' said Daniel Twining , the German Marshall Fund 's senior fellow for Asia . `` He should also make clear that the United States will not countenance aggression against any territory covered by the U.S.-Japan Security Treaty and commit to working closely with Japan to meet security challenges across Asia , starting with North Korea . ''
NEW : The United States will defend itself and its allies if needed , Kerry says . Comment: His three host nations all have new leaders .