Updated 9:33 PM ET
A U.S. official confirmed Thursday that North Korea's nuclear capability is further advanced than previously believed.
As CBS News correspondent David Martin reported, near the end of a long hearing on the defense budget, Congressman Doug Lamborn surprised everyone -- including the secretary of defense and chairman of the joint chiefs -- when he read aloud from a report by the Pentagon's defense intelligence agency.
"This is unclassified, so I can make this public," said Lamborn. "'DIA assess with moderate confidence the north currently has nuclear weapons capable of delivery by ballistic missiles. However, the reliability will be low."
In a statement late Thursday, Pentagon press secretary George Little said: "While I cannot speak to all the details of a report that is classified in its entirety, it would be inaccurate to suggest that the North Korean regime has fully tested, developed or demonstrated the kinds of nuclear capabilities referenced" in Lamborn's remarks.
"The United States continues to closely monitor the North Korean nuclear program and calls upon North Korea to honor its international obligations," Little added.
Additionally James Clapper, director of National Intelligence, said in a statement that he concurred with the previous Pentagon statement. He also added that "the statement read by the Member (Lamborn) is not an Intelligence Community assessment. Moreover, North Korea has not yet demonstrated the full range of capabilities necessary for a nuclear armed missile."
The DIA conclusion was confirmed by a senior congressional aide who spoke on condition of anonymity because the Pentagon had not officially released the contents. The aide said the report was produced in March.
North Korea is known to have enough nuclear material for about a dozen weapons. But until now, no intelligence agency has said publicly the north could make the weapons small enough to put on the tip of a missile, reports Martin.
However, when North Korea conducted a nuclear test last February, it boasted it had a miniaturized device. Add that to last December's launch of a long range missile capable of reaching the U.S., and there is a potential threat which Joint Chiefs Chairman Gen. Martin Dempsey said can not be ignored.
"In the absence of concrete evidence to the contrary," he said, "we have to assume the worst case and that's why we're postured as we are today."
Notably absent from that unclassified segment of the report was any reference to what the DIA believes is the range of a missile North Korea could arm with a nuclear warhead. Much of its missile arsenal is capable of reaching South Korea and Japan, but North Korean leader Kim Jong Un has threatened to attack the United States as well.
North Korea appears ready to launch two intermediate-range missiles. The U.S. has positioned missile defense ships in the Pacific to intercept then, although the top commander there says he does not intend to shoot unless they are headed for targets on land.
Regarding the intel report from DIA saying that it had moderate confidence that the North Koreans miniaturized a nuclear warhead, Martin explained it means there is no smoking gun. However, he added that there is credible evidence to make a plausible case that the North Koreans have figured out how to put a warhead on top of a missile.
Earlier Thursday, North Korea delivered a fresh round of rhetoric with claims it had "powerful striking means" on standby for a launch, while Seoul and Washington speculated that the country is preparing to test a medium-range missile during upcoming national celebrations.
CBS News correspondent Margaret Brennan, reporting from Seoul, South Korea, said on "CBS This Morning" Thursday that conflicting reports say missile launchers have been moved into a firing position.
Brennan reports that, according to U.S. intelligence, North Korea is fully ready to fire off a missile called the Musudan, which is also known as the Taepodong-X. That type of weapon is capable of hitting U.S. military bases in Japan and Guam.
On Thursday, the Taiwanese government became the first country to tell its citizens not to travel to South Korea due to rising tensions, Brennan reports. On Friday, U.S. Secretary of State John Kerry is expected to arrive in Seoul to meet with South Korean officials to try to calm those tensions.
On the streets of Pyongyang, meanwhile, North Koreans celebrated the anniversary of leader Kim Jong Un's appointment to the country's top party post one in a slew of titles collected a year ago in the months after father Kim Jong Il's death.
The Committee for the Peaceful Reunification of the Fatherland, a nonmilitary agency that deals with relations with South Korea, didn't elaborate on its warning of a strike. The statement is the latest in a torrent of warlike threats seen outside Pyongyang as an effort to raise fears and pressure Seoul and Washington into changing their North Korea policy.
A missile launch by North Korea would violate U.N. Security Council resolutions prohibiting the isolated nation from nuclear and ballistic missile activity, and mark a major escalation in Pyongyang's standoff with neighboring nations and the U.S.
North Korea already has been punished in recent months for launching a long-range rocket in December and conducting an underground nuclear test in February.
Analysts do not believe North Korea will stage an attack similar to the one that started the Korean War in 1950. But there are concerns that the animosity could spark a skirmish that could escalate into a serious conflict.
"North Korea has been, with its bellicose rhetoric, with its actions ... skating very close to a dangerous line," U.S. Defense Secretary Chuck Hagel said in Washington on Wednesday. "Their actions and their words have not helped defuse a combustible situation."
Bracing for a launch, which officials said could take place at any time, Seoul deployed three naval destroyers, an early warning surveillance aircraft and a land-based radar system, a Defense Ministry official told The Associated Press in Seoul, speaking on condition of anonymity in line with department rules. Japan deployed PAC-3 missile interceptors around Tokyo.
But officials in Seoul played down security fears, noting that no foreign government has evacuated its citizens from either Korean capital.
"North Korea has continuously issued provocative threats and made efforts to raise tension on the Korean peninsula ... but the current situation is being managed safely and our and foreign governments have been calmly responding," Foreign Ministry spokesman Cho Tai-young told reporters Thursday.
The war talk is seen as a way for North Korea to draw attention to the precariousness of the security situation on the Korean Peninsula and to boost the military credentials of Kim.
The Korean War ended in 1953 with a truce, not a peace treaty, and the U.S. and North Korea do not have diplomatic relations.
For weeks, the U.S. and South Korea have staged annual military drills meant to show the allies' military might. North Korea condemns the drills as rehearsal for an invasion.
Citing the tensions, North Korea on Monday pulled more than 50,000 workers from the Kaesong industrial park, which combines South Korean technology and know-how with cheap North Korean labor. It was the first time that production was stopped at the decade-old factory park, the only remaining symbol of economic cooperation between the Koreas.
South Korea's point man on North Korea, Unification Minister Ryoo Kihl-jae, urged Pyongyang to stop heightening tensions and to discuss the restart of operations in Kaesong.
In Pyongyang, meanwhile, there was no sense of panic. Across the city, workers were rolling out sod and preparing the city for a series of April holidays.
North Korean students put on suits and traditional dresses to celebrate Kim Jong Un's appointment as first secretary of the Workers' Party a year ago.
A flower show and art performances are scheduled over the next few days in the lead-up to the nations' biggest holiday, the April 15 birthday of North Korea founder Kim Il Sung, grandfather of the current leader.
No military parade or mass events were expected over the coming week, but North Korea historically uses major holidays to show off its military power, and analysts say Pyongyang could well mark the occasion with a provocative missile launch in defiance of U.N. Security Council resolutions barring the North from nuclear and missile activity.
"However tense the situation is, we will mark the Day of the Sun in a significant way," Kim Kwang Chon, a Pyongyang citizen, told The AP, referring to the April 15 birthday. "We will celebrate the Day of the Sun even if war breaks out tomorrow."
During last year's celebrations, North Korea failed in an attempt to send a satellite into space aboard a long-range rocket. The U.S. and its allies criticized the launch as a covert test of ballistic missile technology.
A subsequent test in December was successful, and that was followed by the country's third underground nuclear test on Feb. 12, possibly taking the regime closer to mastering the technology for mounting an atomic weapon on a missile.