North Korea says it will restart its uranium enrichment programme and "weaponise" all the plutonium in its possession.
The warning from North Korea's Foreign Ministry was carried by the official Korean Central News Agency today.
It came hours after the UN Security Council approved tough new sanctions on the North to punish it for its latest nuclear test on May 25th.
The sanctions resolution banned all weapons exports from North Korea and most arms imports into the state. It authorised UN member states to inspect North Korean sea, air and land cargo, requiring them to seize and destroy any goods transported in violation of the sanctions.
North Korea today also threatened to take "resolute military action" if the United States or its allies try to impose any "blockade" on it. It did not elaborate if the blockade refers to an attempt to stop its ships or impose sanctions.
North Korea has raised tension in the region in the past months by test-firing missiles, restarting a plant to produce arms-grade plutonium and holding the May 25th nuclear test, which put it closer to having a working nuclear bomb.
South Korea's defence minister said this week the North's sabre rattling is to build internal support for leader Kim Jong-il (67) as he prepares for succession in Asia's only communist dynasty.
Since Kim took over in 1994 and launched his guiding "military first" policy, the North's economy has grown weaker and an estimated 1 million people died in a famine in the late 1990s.
North Korea has been readying a missile that could hit US territory for a test launch by as early as this month and could also test fire mid-range missiles that can strike all of South Korea and most of Japan, South Korean officials have said.
Agencies