After cancelling all non-aggression agreements with South Korea, North Korean officials continue to maintain that the country could carry out a preemptive nuclear strike against the U.S.
The Security Council unanimously imposed new sanctions on North Korea on Friday, tightening financial restrictions and cracking down on its attempts to transport banned cargo.
The North's sole major ally China wants the sanctions fully implemented. The sanctions are designed to make punitive measures more like those used against Iran, which Western officials say have been surprisingly successful.
"The DPRK, as it did in the past, vehemently denounces and totally rejects the 'resolution on sanctions' against the DPRK, a product of the U.S. hostile policy toward it," the North's foreign ministry spokesman said in a statement.
DPRK is short for the North's official name, the Democratic People's Republic of Korea.
The UN Security Council passes new sanctions on North Korea in the face of nuclear threats from the country's leaders. NBC's Kurt Gregory reports.
The United States warned North Korea it will achieve nothing by repeating threats of provocative actions and will only drive itself deeper into international isolation.
"The United States of America and our allies are prepared to deal with any threat and any reality that occurs in the world," U.S. Defence Secretary Chuck Hagel said ahead of his visit to Afghanistan on Friday. "We are aware of what's going on. We have partnerships in that part of the world that are important."
North Korea defied international warnings and conducted a third nuclear test in February, setting off a device that yielded a stronger blast than its previous test in 2009. It claimed it had made progress in miniaturizing an atomic weapon.
Experts are skeptical of such a claim, and the threat this week to attack the United States, seeing them more as an attempt to boost its security leverage in the face of deepening diplomatic isolation and growing military pressure from the United States and South Korea, which are conducting joint military drills to deter any armed aggression from Pyongyang.
Experts believe the North is still years away from developing the capability to deliver a nuclear weapon to the United States but say it can strike South Korea or Japan using its short and medium-range missiles.
North Korea has accused the United States of using military drills in South Korea as a launch pad for a nuclear war and declared on Tuesday it would scrap the armistice with Washington that ended hostilities in the 1950-53 Korean War.
The two Koreas are technically at war because the armistice and not a formal peace treaty ended their 1950-53 conflict.
South Korea and U.S. forces are conducting large-scale military drills until the end of April. The North is also gearing up for a massive state-wide military exercise.
Pyongyang's soaring anti-American rhetoric is seen by experts as a ploy to be taken as a serious threat and to force Washington back to the negotiating table.
A more likely option for Pyongyang than a full-scale conflict is to stage a series of clashes along a disputed frontier with the South, a sea border known as the Northern Limit Line, which has been the scene of previous clashes.
Tensions on the Korean peninsula have growing since the sinking of a South Korean navy ship in March 2010 widely blamed on North Korea, although Pyongyang denies responsibility. The North in November that year bombed a South Korean island killing two civilians.