Last Updated 2:45 p.m. ET
SEOUL, South Korea U.S. Secretary of State John Kerry delivered a stark warning to North Korea on Friday not to test-fire a mid-range missile, while rejecting a new U.S. intelligence report suggesting significant progress in the communist regime's nuclear weapons program.
Appearing Friday at a joint news conference with South Korea's foreign minister, Kerry said the United States would not accept the North as a nuclear power, adding that the war-like rhetoric of the Kim Jong-Un regime is unacceptable.
"We are all united in the fact that North Korea will not be accepted as a nuclear power," Kerry said. "The rhetoric that we're hearing from North Korea is simply unacceptable."
Kerry arrived in South Korea on a diplomatic mission to lower rising tensions in a region bracing for a possible North Korean missile launch or nuclear test. It marked the kickoff of four days of talks in East Asia amid speculation that the North's unpredictable regime would launch a mid-range missile designed to reach as far as the U.S. territory of Guam.
The Secretary of State told reporters in Seoul that Pyongyang and its enigmatic young leader would only increase their isolation if they launched the missile that American officials believe has a range of some 2,500 miles -- or enough to reach the U.S. territory of Guam.
"If Kim Jong Un decides to launch a missile, whether it's across the Sea of Japan or some other direction, he will be choosing willfully to ignore the entire international community," Kerry told reporters. "And it will be a provocation and unwanted act that will raise people's temperatures."
Kerry said the test would be a "huge mistake" for Kim.
"It will further isolate his country and further isolate his people who are desperate for food and not missile launches," he warned. "They are desperate for opportunity and not for a leader to flex his muscles."
South Korean Foreign Minister Yun Byung-se called Pyongyang's threats a "grave provocation" to the entire international community.
Within hours of Kerry's arrival, Pyongyang issued a warning that Japan, a U.S. ally, will be the first target if war breaks out on the Korean peninsula.
CBS News correspondent Margaret Brennan reports Kerry will travel to Beijing Saturday to push China to cut its extensive financial ties to President Kim Jong-Un's regime. Despite those ties, China is struggling to find a way to influence North Korea, Brennan said.
Kerry's trip coincides with the disclosure of a U.S. military intelligence report that concluded North Korea has advanced its nuclear know-how to the point that it could arm a ballistic missile with a nuclear warhead. The analysis, disclosed Thursday at a congressional hearing in Washington, said the Pentagon's intelligence wing has "moderate confidence" that North Korea has nuclear weapons capable of delivery by ballistic missiles but that the weapon would be unreliable.
Pentagon spokesman George Little said afterward, however, that "it would be inaccurate to suggest that the North Korean regime has fully tested, developed or demonstrated the kinds of nuclear capabilities referenced" at the congressional hearing.
James Clapper, the director of national intelligence, said he concurred with Little, and noted that the report alluded to at the hearing was compiled by the Pentagon's Defense Intelligence Agency and was not an assessment by the entire U.S. intelligence community. "Moreover, North Korea has not yet demonstrated the full range of capabilities necessary for a nuclear armed missile," he said.
Speaking Friday in Seoul to journalists traveling with Kerry, a senior U.S. official said it would be "premature" to say the North Koreans had gained the ability to miniaturize a nuclear weapon sufficiently to mount it on a ballistic missile. CBS News correspondent Margaret Brennan said the official described the process of miniaturization as a "very, very difficult task."
On Friday White House spokesperson Jay Carney also said that it is the administration's assessment that "North Korea has not demonstrated the capability to deploy a nuclear-armed missile."
Carney also said that the United States continues to closely monitor North Korea's nuclear program, "and calls upon North Korea to honor its international obligations."
South Korea agrees that Pyongyang does not yet have a nuclear device small enough to put on a missile, Defense Ministry spokesman Kim Min-seok said Friday, in response to a question about the DIA assessment.
"Our military's assessment is that North Korea has not yet miniaturized" a nuclear device, Kim said.
President Obama on Thursday urged calm, calling on Pyongyang to end its saber-rattling while sternly warning that he would "take all necessary steps" to protect American citizens.
Kerry's trip marks his first foray to the Asia-Pacific as America's top diplomat, spearheading the effort to "pivot" U.S. power away from Europe and the Middle East and toward the world's most populous region and fulcrum of economic growth.
It comes on the heels of months of provocative action and war-like rhetoric from Pyongyang, including talk of nuclear strikes against the United States -- however outlandish analysts consider such threats. No one is discounting the danger entirely after tests of a nuclear device and ballistic missile technology in recent months.
The U.S. official in Seoul told reporters that current anxiety was pegged to North Korean leader Kim Jong Un's youth and inexperience, which make him "very vulnerable to miscalculation."
Asked, however, whether the U.S. government believed war on the Korean peninsula was imminent, Brennan said the official responded decisively: "Not at all."
Kerry's trip was planned well in advance of the latest danger to destabilizing the Korean peninsula: North Korea's apparent preparations for another missile test in defiance of United Nations resolutions. The crisis clearly has overtaken the rest of his Asian agenda.
The Obama administration believes North Korea is preparing for another missile test, said a senior State Department official traveling with Kerry on the plane to Seoul. "We will show to our allies that we are prepared and we will defend them," the official said.
To mitigate the threat, however, Kerry is largely depending on China to take a bigger role in pressuring North Korea to live up to previous agreements to halt its nuclear and ballistic missile programs. It's a strategy that has worked poorly for the U.S. for more than two decades.