North Korea on Saturday threatened "resolute military action" if the United States tried to isolate it after the U.N. Security Council imposed widened sanctions against the reclusive communist state for a nuclear test in May.
The North also vowed to start a program to enrich uranium and to "weaponize" plutonium at its nuclear weapons plant, the North's official news agency KCNA quoted its foreign ministry spokesman as saying.
The report said Pyongyang would consider any attempt by U.S. or its allies to impose a "blockade" as an "act of war."
The sanctions resolution approved on Friday banned all weapons exports from North Korea and most arms imports into the state. It authorized U.N. 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.
Secretary of State Hillary Rodham Clinton said the latest U.N. penalties provide the tools needed "to take appropriate action" against the communist nation.
Clinton said the U.S. was gratified at the latest move against North Korea, adding that action represented a unified response against the North's provocative action.
She said the U.S. will work with other countries on vigorously enforcing the sanctions. She said he goal is to send a clear message about preventing nuclear proliferation by the North.
North Korea's response?
A senior South Korean official said that North Korea may possibly respond to U.N. punishment with "another nuclear test and maybe more missiles."
"They will never, never give up their nuclear weapons," said the official who asked not to be named due to the sensitive subject matter.
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 25 nuclear test, which put it closer to having a working nuclear bomb.
Two senior diplomats negotiating the U.N. resolution told Reuters on condition of anonymity the Chinese had never really clarified whether they intended to implement the new sanctions resolution.
China's U.N. ambassador, Zhang Yesui, said the resolution showed the "firm opposition" of the international community to North Korea's nuclear ambitions, but he urged countries to exercise caution when inspecting North Korean cargo.
"Under no circumstances should there be use or threat of the use of force," Zhang said.
'United' international response
The resolution seeks to deprive North Korea of financing and material for its weapons program and bans the country's lucrative arms exports, especially missiles. It does not ban normal trade, but does call on international financial institutions not to provide the North with grants, aid or loans except for humanitarian, development and denuclearization programs.
U.S. Deputy Ambassador Rosemary DiCarlo said the resolution provides "a strong and united international response" to North Korea's test in defiance of a ban imposed after its first underground atomic blast in October 2006.
Studies have shown that U.N. sanctions imposed on North Korea for missile testing and its only prior nuclear test in 2006 had almost no impact, while its meager trade actually increased due to lax enforcement of those measures.
"The success of financial sanctions depends heavily on how far China and the United States are willing to go to pressure North Korea," said Jeong Hyung-gon, a research fellow at the Korea Institute for International Economic Policy.
The isolated country's $2 billion annual trade with neighboring China, equal to about 10 percent of the North's annual GDP, is its most important economic relationship. Beijing has wanted to avoid any measures that could cause the North's economy to collapse and lead to chaos on its border.
South Korea's defense minister said this week the North's saber 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 will be high on the agenda when South Korean President Lee Myung-bak goes to Washington this week for a summit with President Barack Obama.
"One of the most important reasons for North Korea continuing its nuclear ambitions is to consolidate the power to stay within the Kim Jong-il family," Lee said in an interview with the Wall Street Journal.
The new U.N. measures expand previous provisions to hit North Korea's arms trade, which is a key source of foreign currency for the destitute state that produces few other goods it can sell to the outside world.
A study by the U.S.-based Institute for Foreign Policy Analysis think tank this year estimated Pyongyang earns around $1.5 billion a year from missile sales.
During more than two weeks of negotiations on the draft resolution, the United States and Japan had pushed to authorize forced inspections of suspicious air, land and sea cargo. But diplomats said Russia and China had made clear they would veto the resolution unless the inspections were based on consent.
The resolution did speak of a "required inspection" if a ship refuses to be inspected. But the ship's flag country could then send the vessel to any port it chooses, where the local authorities would carry out any cargo inspection.
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