North Korea announced on Monday it would bolster its nuclear arsenal in a "newly developed way" in response to perceived US hostility, reports said.
Tensions have been rising on the Korean Peninsula since the sinking of a South Korean warship near the maritime border in March, which investigators blamed on a North Korean torpedo, a charge the Stalinist state denies.
"The recent disturbing development on the Korean Peninsula underscores the need for the DPRK to bolster its nuclear deterrent in a newly developed way," a spokesman for the Foreign Ministry was quoted as saying by Pyongyang's Korean Central News Agency KCNA.
The Democratic People's Republic of Korea, or DPRK, is North Korea's official name.
The move was provoked by "US persistent hostile policy" and "military threat" to North Korea, the spokesman said.
The report did not provide further details of the new developments.
In September, the communist country announced it had almost completed the experimental phase of its uranium enrichment programme.
Highly enriched uranium is a key component of nuclear weapons, while low enriched uranium is used to make nuclear fuel.
The US have suspected North Korea for years of conducting uranium-enrichment programmes, in addition to the plutonium production drive that formed the basis for its two successful nuclear weapons tests to date.
Pyongyang's statement came shortly after the de-classification of 1969 US documents outlining the possibility of a "tactical" nuclear strike against North Korea in response to provocation.
The KCNA report said the revealed documents showed that the US was still seeking excuses to drop nuclear weapons on North Korea.