The announcement came amid North Korean attempts to pressure the US into accepting its demand for direct talks.
Washington said it is willing to meet one-on-one with the North if it leads to the resumption of six-party talks involving China, Japan, the two Koreas, Russia and the US, but it has not made any decision on whether to hold direct talks.
North Korea restarted its nuclear facilities at its Yongbyon complex in April in anger over a UN rebuke of its rocket launch, which was denounced as a test of its long-range missile technology.
KCNA said the UN censure of what it called a peaceful satellite launch "was a grave insult to the dignity of its people".
It said it was compelled to bolster "its deterrent for self-defence to cope with the increasing nuclear threat and military provocations of the hostile forces".