US disarmament ambassador Robert Wood, addressing the UN-sponsored Conference on Disarmament in Geneva, also warned that arsenals in China and Russia were expanding, Reuters reported.
"Russia, China and North Korea are growing their stockpiles, increasing the prominence of nuclear weapons in their security strategies, and - in some cases - pursuing the development of new nuclear capabilities to threaten other peaceful nations," he said.
North Korea "may now be only months away from the capability to strike the US with nuclear-armed ballistic missiles".