The United States on Thursday insisted North Korea did not have nuclear-armed missiles as officials sought to play down a leaked intelligence report warning Pyongyang had likely succeeded in building atomic warheads that could be fit on a ballistic missile.

Pentagon spokesman George Little said "it would be inaccurate to suggest that the North Korean regime has fully tested, developed, or demonstrated the kinds of nuclear capabilities referenced in" the intelligence report.

The statement came after a lawmaker read out the findings of a Defense Intelligence Agency (DIA) report at a congressional hearing earlier Thursday that appeared to signal a shift in Washington's view of North Korea's nuclear program.

The DIA assessment said US analysts had "moderate confidence the North currently has nuclear weapons capable of delivery by ballistic missiles" but that the reliability of the weapons was "low."

The intelligence report marked the first time the US government had suggested North Korea may have succeeded in a years-long quest to miniaturize a nuclear device so that it could be placed on a missile.

Defense Secretary Chuck Hagel and the US military's top officer, General Martin Dempsey, appeared caught off-guard when the report's findings were disclosed at a hearing of the House Armed Services Committee.

After the hearing, administration officials scrambled to explain what appeared to be a change in the government's portrayal of the North Korean threat.

A senior US official, who spoke on condition of anonymity, told AFP that the administration had not changed its evaluation that Pyongyang was still not at a point where it could deliver a nuclear warhead on a ballistic missile.

"The North Koreans have never demonstrated this capability and we don't believe they are able to now," the official said.

The confusion over the spy agency report came against the backdrop of mounting tensions on the Korean peninsula, with Pyongyang issuing bellicose threats and preparing to possibly launch medium-range missiles.

The Pentagon, which has bolstered missile defenses around the Korean peninsula, said it was closely watching North Korea amid speculation the regime would fire conventional missiles in the run-up to national celebrations on April 15th.

"The United States continues to closely monitor the North Korean nuclear program and calls upon North Korea to honor its international obligations," Little said.

Kerry heads to S.Korea as tensions soar
London (AFP) April 11, 2013 - US Secretary of State John Kerry was headed for South Korea Thursday on his maiden trip to Asia in a show of American support for regional allies as tensions soar over a feared new missile test by the North.

The volatile situation on the Korean peninsula fuelled by a series of bellicose statements by Pyongyang was one of the global crises crowding the agenda for Kerry's two-day talks in London with G8 foreign ministers.

North Korea has threatened nuclear strikes against the United States and South Korea, and observers expect a missile launch could happen at any time.

The G8 foreign ministers condemned North Korea's nuclear moves "in the strongest possible terms", they said in a statement ahead of Kerry's departure from Britain.

Pyongyang was Thursday marking the first anniversary of new leader Kim Jong-Un taking over as head of the ruling Worker's Party, and any launch could be timed to seize the limelight as Kerry arrives on the divided peninsula.

Monday will also be the birthday of Kim's grandfather and the late founder of the communist state Kim Il-Sung -- an occasion which is usually marked with lavish celebrations.

Kerry, who only took over as the top US diplomat on February 1, has denounced Pyongyang's actions, including a threat to reopen an uranium enrichment facility, as "provocative."

The United States has already bolstered its missile defenses in the region to help protect allies South Korea and Japan as well as US bases in Guam, while US and South Korean forces are on alert.

Kerry is due to be briefed first-hand on the tensions when he arrives in Seoul from top US military commanders on the ground, ahead of meetings with new South Korean President Park Geun-Hye and Foreign Minister Yun Byung-Se.

"North Korea... with its bellicose rhetoric, its actions, has been skating very close to a dangerous line," US Defence Secretary Chuck Hagel has said.

Kerry's whirlwind three-day trip is his first to Asia since becoming secretary of state and he will also make stops in China and Japan on what is being seen by observers as a "getting to know you" tour.

Despite being a veteran of the Vietnam war and a long-time member of the Senate foreign relations committee, he has not travelled much to the region in recent years and does not have close ties with Asian leaders.

Saturday's visit to Beijing will be key, with Kerry expected to try to press Chinese leaders including Chinese Foreign Minister Wang Yi to do more to rein in their ally and neighbour, North Korea.

Washington "would hope that China would do a lot of things to restrain the flow of energy and food to North Korea... hold back on new investment," said expert Douglas Paal from the Carnegie Endowment for International Peace.

The problem is that "those all run against China's primary interest to North Korea which is to provide for stability there."

But with a new level of debate being seen in China about what to do with North Korea, "it's worth putting our views forward and hope to tilt the debate in our direction," Paal added in a recent conference call.

As all sides seek to stop the situation from spiralling out of control, experts also say it might be time to revisit the 1953 armistice which ended the Korean War with a ceasefire pact, rather than a full peace treaty.

Carnegie expert James Schoff called the armistice "tattered and frayed on the edges." Much could be done to "update the armistice" and help "reduce tension or the potential for conflict or accidental conflict on the DMZ," he said.

Kerry's final stop will be in Japan for talks on Sunday and Monday, before flying back to Washington.