North Korea vowed Saturday to step up its atomic bomb-making program and threatened war if its ships are stopped as part of new U.N. sanctions aimed at punishing the nation for its latest nuclear test.

North Korea’s Foreign Ministry also acknowledged for the first time that the country has a uranium enrichment program, and insisted it will never abandon its nuclear ambitions. Uranium and plutonium can be used to make atomic bombs.

The threats, in a statement issued through the official Korean Central News Agency, came a day after the Security Council approved new sanctions aimed at depriving the North of the financing used to build its rogue nuclear program.

The resolution also authorized searches of North Korean ships suspected of transporting illicit ballistic missile and nuclear materials.

The sanctions are “yet another vile product of the U.S.-led offensive of international pressure aimed at undermining … disarming DPRK and suffocating its economy,” the North Korean statement said.

Pyongyang blamed Washington for the nuclear tensions, saying it was “compelled to go nuclear in the face of the U.S. hostile policy and its nuclear threats.”

Washington says it has no intention of attacking the North and said its concern is that North Korea is trying to sell its nuclear technology to other nations.

Saturday’s threats made clear North Korea’s refusal to back down from international calls to give up its nuclear ambitions in the wake of its April rocket launch and underground nuclear test last month.

The statement also raised concerns of a military skirmish.

“An attempted blockade of any kind by the U.S. and its followers will be regarded as an act of war and met with a decisive military response,” the North said.

As a precaution, South Korea has dispatched hundreds more marines to two islands near a western maritime border with North Korea that was the scene of deadly naval clashes in 1999 and 2002, officials said Friday.

North Korea’s acknowledgment that it has a uranium-enrichment program appears to confirm that it has a second source of bomb-making materials in addition to plutonium.

North Korea is believed to have about 110 pounds (50 kilograms) of plutonium, enough for half a dozen bombs, Yoon Deok-min, a professor at South Korea’s state-run Institute of Foreign Affairs and National Security, said Saturday.

Reprocessing 8,000 spent nuclear fuel rods stored at North Korea’s Yongbyon complex could yield additional 18 to 22 pounds (8-10 kilograms) of plutonium — enough to make at least one more atomic bomb, he said.

More than a third of the spent fuel rods have been reprocessed and the rest of its plutonium will be weaponized, North Korea said Saturday.

Those moves would mark a significant step away from a disarmament pact between North Korea and five other nations in wake of its first nuclear test in 2006.

Under the deal, North Korea agreed to disable its main nuclear complex in Yongbyon north of Pyongyang in return for 1 million tons of fuel oil and other concessions. In June 2008, North Korea blew up the cooling tower there in a dramatic show of its commitment to denuclearization.

But disablement came to halt a month later as Pyongyang wrangled with Washington over how to verify its past atomic activities. The latest round of talks, in December, failed to push the process forward. The negotiations involve China, Japan, the two Koreas, Russia and the U.S.

North Korea walked away from the talks in April after the Security Council condemned its April 5 rocket launch, seen by the U.S., Japan and others as a cover for a long-range missile test.

North Korea has said it will test another long-range missile and is suspected of preparing for a third nuclear test, but there is no evidence that either plan is imminent.

Washington had anticipated a strong North Korean response to the U.N. sanctions. Susan Rice, U.S. ambassador to the United Nations, cautioned Friday that North Korea could react to the resolution with “further provocation.”

“There’s reason to believe they may respond in an irresponsible fashion to this,” she told reporters.

Analyst Kim Yong-hyun of Seoul’s Dongguk University said North Korea was sending a stern message to Washington before President Barack Obama sits down with South Korea’s Lee Myung-bak for summit talks at the White House on Tuesday.

He said North Korea is engaging in a game of “chicken” with the U.S. that he predicted would eventually end in talks.

Tags: Atomic Bomb, Atomic Bombs, Ballistic Missile, Central News Agency, Hostile Policy, Korean Central News, Korean Central News Agency, Military Response, North Korea, Nuclear Ambitions, Nuclear Materials, Nuclear Technology, Nuclear Tensions, Nuclear Test North Korea, Nuclear Threats, Rocket Launch, South Korea, Two Islands, Underground Nuclear Test, Uranium Enrichment Program