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PYONGYANG, North Korea — North Korea has warned that it may carry out further nuclear tests and says it is prepared to launch a preemptive strike on the United States if U.S. nuclear forces mobilize against it.

"The U.S. has nuclear weapons off our coast, targeting our country, our capital and our Dear Leader, Kim Jong Un," a top North Korean official, Lee Yong Pil, said in an exclusive interview with NBC News.

"We will not step back as long as there's a nuclear threat to us from the United States," added Lee, who is director of the Foreign Ministry's Institute for American Studies.

"A preemptive nuclear strike is not something the U.S. has a monopoly on," he said. "If we see that the U.S. would do it to us, we would do it first. ... We have the technology."

Such threats have been a staple of North Korean leader Kim Jong Un since he took power after his father's death in 2011. U.S. officials do not believe Pyongyang possesses weapons able to reach the continental United States.

Lee also warned that North Korea may carry out "a sixth, a seventh or an eighth" nuclear test.

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Lee said his government's stance was being driven by "the increasingly aggressive" drills by the United States and the South.

The comments came as Washington and Seoul conducted joint naval exercises off the Korean peninsula. The South Korean military told the country's Yonhap news agency that one of the drills scheduled to end later this monthinvolved targeting the North's nuclear facilities.

For its part, North Korea has accelerated its nuclear program, carrying out its fourth and fifth tests this year. The International Atomic Energy Agency called the moves "deeply troubling" and "regrettable."

Putting the world on notice of another nuclear test would anger the international community, most of which is already considering further sanctions against the reclusive nation for its activity so far.

Lee said neither sanctions from the United Nations nor U.S. pressure would stop North Korea's building its arsenal.

"We have to have nuclear weapons to protect our country, and it's our policy to go nuclear," he added.

Related: Inside North Korea's DMZ, the Front Line of Unfinished War

Another North Korean official told NBC News that the reclusive nation already has the capability to reach the U.S. mainland with a rocket. Hwang Yongnam, who is authorized to speak about the country's missile program, said the Pentagon is lying when it says the North cannot yet reach the continental United States with a weapon.

But it's not just weapons the country's interested in, according to Ri Won Hyok, a senior official involved in North Korea's fledgling space program.

Ri said that Pyongyang is also launching rockets to carry satellites into space and that "in the future our goal is not just going to the moon, but to the other planets."

He denied that the country's rocket program has had help from Russia or Iran, claiming "it's 100 percent our own."

U.S. scientists believe that none of North Korea's launches so far have included any fully functioning satellites.