North Korean leader Kim Jong Un on Friday claimed the U.S. mainland is now within range of his country's nuclear weapons, according to a report from Public Radio International (PRI).

The statement comes after North Korea successfully tested its first submarine-launched missile.

But a former U.S. nuclear negotiator with North Korea, Joel Wit, told PRI the U.S. is not in danger.

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"We’re not within striking range of their nuclear weapons," he said.

Wit said there is ground for alarm over North Korea's nuclear development, however.

"This is just one more step in terms of steady progress that North Korea is making in building nuclear weapons and building missiles to deliver them.”

He said the larger worry should be North Korea's current Intercontinental Ballistic Missile (ICBM) project.

“I’m concerned, and I think it should be ongoing concern for everyone,” he said. “If they get that thing [ICBM] working then they will be able to reach the United States, and that, of course, is a serious concern for all of us."

As of today, North Korea does not possess the ability to miniaturize their nuclear weapons into a small warhead or launch their missiles beyond a range of 600 miles the report added.