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

The North's warning came two days after the U.N. Security Council unanimously approved new sanctions to punish the North including a ban on coal and other exports worth over $1 billion. U.S. Ambassador 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. The North said it will take "action of justice" but didn't elaborate.

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 are capable of reaching parts of the United States if fired at a normal, flattened trajectory.

The centerpiece of the U.N. sanctions is a ban on North Korea exports of coal, iron, lead and seafood products — and a ban on all countries importing these products, estimated to be worth over $1 billion in hard currency.

According to a Security Council diplomat, coal has been North Korea's largest export, earning $1.2 billion last year which was then restricted by the Security Council in November to a maximum $400 million. This year, Pyongyang was estimated to earn $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 council diplomat was not authorized to speak publicly and insisted on anonymity.