SEOUL, South Korea — North Korea vowed Monday to bolster its nuclear arsenal and launch "thousands-fold" revenge against the United States in response to tough U.N. sanctions imposed after its recent intercontinental ballistic missile launches.

The warning came two days after the U.N. Security Council unanimously approved new sanctions to punish North Korea, including a ban on coal and other exports worth over $1 billion. The U.S. ambassador to the U.N., Nikki Haley, called the U.S.-drafted resolution "the single largest economic sanctions package ever leveled against" North Korea.

In a statement carried by state media, the North Korean government said the sanctions were a "violent infringement of its sovereignty" that was caused by a "heinous U.S. plot to isolate and stifle" North Korea.

It said the U.N. sanctions will never force the country to negotiate over its nuclear program or to give up its push to strengthen its nuclear capability as long as U.S. hostility and nuclear threats persist. The North said it will take an "action of justice," but didn't elaborate.

"It's a wild idea to think the DPRK will be shaken and change its position due to this kind of new sanctions formulated by hostile forces," said the statement, carried by the North's official Korean Central News Agency. DPRK stands for the North's official name, the Democratic People's Republic of Korea.

The North's statement "rhetorically expresses its anger" against the U.N. sanctions, but the country is not likely to launch a direct provocation against the United States, said Lim Eul Chul, a North Korea expert at South Korea's Kyungnam University. He said the North could still carry out new missile tests or a sixth atomic bomb test in the coming months under its broader weapons development timetable.

North Korea test-launched two ICBMs last month as part of its efforts to possess a long-range missile capable of striking anywhere in the mainland U.S. Both missiles were fired at highly lofted angles and analysts say the weapons could reach parts of the United States including Alaska, Los Angeles and Chicago if fired at a normal, flattened trajectory.

The centerpiece of the U.N. sanctions is a ban on North Korean exports of coal, iron, lead and seafood products — and a ban on all countries importing those products, estimated to be worth over $1 billion a year in hard currency. The resolution also bans countries from giving any additional permits to North Korean laborers, another source of foreign currency for the North, and prohibits all new joint ventures with North Korean companies.

According to a Security Council diplomat, coal has been North Korea's largest export, earning $1.2 billion last year. It was then restricted by the Security Council in November to a maximum of $400 million. This year, Pyongyang is estimated to have earned $251 million from iron and iron ore exports, $113 million from lead and lead ore exports, and $295 million from fish and seafood exports, the diplomat said. The diplomat was not authorized to speak publicly and insisted on anonymity.

Analysts say that North Korea, already under numerous U.N. and other international sanctions, will feel some pains from the new U.N. sanctions but won't likely return to disarmament negotiations anytime soon because of them.

Lim, the North Korea expert, said the North will likely squeeze its ordinary citizens to help finance its nuclear and missile programs. Shin Beomchul of the Seoul-based Korea National Diplomatic Academy said the North won't likely return to disarmament talks unless there are sanctions that require China to stop sending its annual, mostly free shipment of 500,000 tons of crude oil to North Korea and order U.N. member states to deport the existing tens of thousands of North Korean workers dispatched abroad.

Associated Press writer Edith M. Lederer at the United Nations contributed to this report.