The North Korean army has said it has received final approval to launch "merciless" military strikes on threats from the US, involving the possible use of "cutting edge" nuclear weapons, a statement said on the country's KCNA news agency.
The General Staff of the Korean People's Army said it was informing Washington that US threats would be "smashed by...cutting-edge smaller, lighter and diversified nuclear strike means".
The statement added: "The merciless operation of (our) revolutionary armed forces in this regard has been finally examined and ratified."
US Defence Secretary Chuck Hagel confirmed that the US was taking North Korea's threats "seriously" and said the country posed a "real and clear" danger.
Through her tears, a North Korean woman told me how she had to escape: risk death while running across the border or die of starvation.
Memories of the Korean war are never far away in South Korea, where residents have grown used to living with the constant threat of war.
North Korea said it will withdraw workers from the Kaesong factory park run jointly with South Korea and suspend all operations there.