SEOUL, South Korea — 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 nuclear program.

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

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.

North Korea walked away from 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.