Mattis warns North Korea of 'end of its regime,' 'destruction of its people'

— -- U.S. Secretary of Defense James Mattis cautioned Wednesday that North Korea's actions "will continue to be grossly overmatched by ours and would lose any arms race or conflict it initiates," a day after President Donald Trump issued a similar warning in the wake of reports North Korea is continuing to advance its nuclear capabilities.

Mattis added that North Korean leader Kim Jong Un should "take heed" of the United Nations Security Council's "unified voice," referring to recent sanctions issued against the nation, and called for the country to "cease any consideration of actions that would lead to the end of its regime and the destruction of its people."

The comments came in a statement released by the Department of Defense.

On Tuesday, during a briefing about the opioid crisis, Trump warned North Korea to not make any further threats against the United States.

"They will be met with fire and fury like the world has never seen," Trump said. "He [Kim] has been very threatening — beyond a normal statement — and as I said, they will be met with fire, fury and, frankly, power the likes of which the world has never seen before."

Members of the U.S. intelligence community believe that North Korea's nuclear capabilities may be more advanced than initially thought and the country might have developed the technology to miniaturize a nuclear warhead so it can be placed inside an intercontinental ballistic missile, a U.S. official told ABC News on Tuesday. The Washington Post first reported the news, citing a July 28 report by the Defense Intelligence Agency about North Korea's capabilities.

Mattis' statements on Wednesday added to the increasingly heated rhetoric between North Korea and the United States.

Responding to Trump's comments, North Korea said it was considering a strike on Guam that would create "an enveloping fire."

Guam is a U.S. territory in the western Pacific that is home to a key Air Force base.

On his way back from a trip to Asia, Secretary of State Rex Tillerson stopped in Guam for aircraft refueling and responded to Trump's "fire and fury" comment, telling reporters the president was just using language that North Korea understands.

Tillerson added that there were no new threats to Guam.

On July 28, North Korea launched its second ICBM, which had the longest flight of a ballistic missile in the country's history, the Pentagon confirmed.

It has not conducted a nuclear test since September 2016.

ABC News' Luis Martinez contributed to this report.