Nuclear-armed North Korea has a ballistic missile that could hit the United States, the leading lawmaker on the US House of Representatives intelligence committee warned Sunday.

Congressman Mike Rogers also raised concern that North Korea's young leader Kim Jong-Un is trying to prove himself to his military and that Washington could not be sure of his "stability."

"They certainly have a ballistic missile that can reach US shores," Rogers told the CNN news network, without specifying whether he was referring to the more exposed US states of Alaska and Hawaii or to America's west coast.

"You have a 28-year-old leader who is trying to prove himself to the military, and the military is eager to have a saber rattling for their own self-interest, and the combination of that is proving to be very, very deadly."

North Korea has tested missiles that could strike South Korea or Japan but has yet to demonstrate it has the capability to fire long-range missiles that could reach the continental United States.

It is also not clear how close North Korea is to being able to convert one of the nuclear devices that it has tested to function as a missile warhead.

On Friday, the United States said it would beef up its defenses against a possible North Korean missile strike a week after Pyongyang threatened a "pre-emptive" nuclear attack against its arch enemy.

Defense Secretary Chuck Hagel said 14 more interceptors would be stationed in Alaska by 2017, increasing by almost half the number already deployed along the California and Alaska coastlines.

Pyongyang has threatened to unleash a second Korean War -- backed by nuclear weapons -- in response to UN sanctions imposed after its third atomic test last month and to joint South Korea-US military maneuvers.

"This is something that we have to take seriously, and you can see that they're looking for some provocations, not just along the border, but there's some islands that they're interested in," Rogers said.

Rogers acknowledged the United States knew more about Kim's father, Kim Jong-Il, than it does about the country's current head.

"We just don't know the stability" of the 28-year-old, Rogers said.

N. Korea says nukes are not a bargaining chip for aid
Seoul (AFP) March 17, 2013 - North Korea said Sunday it would never trade its nuclear weapons programme for aid and stressed its "unshakeable" stance to retain the deterrent, following a third atomic test last month.

The North's foreign ministry, in a statement carried by state TV, rejected suggestions that the impoverished state was using its weapons programme as a way of bullying neighbours into offering much-needed aid.

"The US is seriously mistaken if it thinks that the (North) had access to nukes as a bargaining chip to barter them for what it called economic reward," it said.

The comments came days after the US National Security Advisor Tom Donilon said Washington was willing to hold "authentic negotiations" with the North if it changed its behaviour.

"To get the assistance it desperately needs and the respect it claims it wants, North Korea will have to change course," he said last week.

But the North Sunday called its atomic weaponry a "treasured sword" to protect itself from what it called a hostile US policy.

The US "temptation" may work on other countries "but it sounds nonsensical" to the North, the foreign ministry statement said.

"The (North) would like to re-clarify its unshakeable principled stand on its nuclear deterrence for self-defence."

Last month's test, its most powerful to date, prompted the United Nations to further tighten sanctions imposed following previous nuclear tests and long-range rocket launches in 2006 and 2009.

The tougher sanctions, and an ongoing South Korean-US military exercise, sparked an angry response from Pyongyang, which said it was tearing up the armistice that ended the Korean War and ending non-aggression pacts with Seoul.

The country has suffered chronic food and fuel shortages for decades, with the situation exacerbated by floods, droughts, mismanagement and global sanctions.

International food aid, especially from South Korea and the US, has been drastically cut over the past several years amid tensions over the North's nuclear and missile programmes.

A six-nation aid-for-denuclearisation forum on the North, involving the two Koreas, China, Japan, the US and Russia, have been at a standstill since the last meeting in December 2008.

Almost 28 percent of the North's children aged under five are stunted from malnutrition, a 2012 UN national nutrition survey showed.