"North Korea must choose to stop isolating itself and stand down its pursuit of nuclear weapons", Mattis said in a written statement, adding that the "regime's actions will continue to be grossly overmatched by ours and would lose any arms race or conflict it initiates".
"What we're trying to do here is [be] loud and clear in the diplomatic arena: It is North Korea's choice", Mattis said.
Trump's advisers offered contradictory statements in an attempt to clarify the president's dire warnings over Pyongyang's nuclear and missile program، highlighting the conflicting views in the White House about how to deal with North Korea، analysts say. In the past he has said that the United States can respond to North Korea, but any military solution would be "tragic on an unbelievable scale".
Tension in the region has risen since North Korea carried out two nuclear bomb tests past year and two intercontinental ballistic missile tests in July. Secretary of Defense James Mattis, one of the more hard-nosed members of Trump's cabinet maintained a tough stance, although far more nuanced, than that of his commander-in-chief.
The KCNA statement came hours after Trump at his estate in Bedminster, N.J., said that North Korea would "face fire and fury like the world has never seen" unless it stopped threatening the USA and its allies. "Its threat on Guam appears to be aimed at boosting internal solidarity", the official said, according to South Korea's Yonhap news agency.
North Korea has repeatedly denounced the THAAD deployment and escalated its threats after the United Nations Security Council voted 15-0 last week to impose tougher sanctions on the North.
Earlier Wednesday, U.S. Secretary of State Rex Tillerson defended Trump's remarks.
It comes following an exchange of threats and boasts of nuclear power by President Donald Trump and North Korea.More news: Egyptian officials: 4 policemen killed in northern Sinai
United States military officials played down the potential for military conflict.
The Washington Post reported on Tuesday, citing US intelligence sources, that North Korea had miniaturized a nuclear warhead that could be mounted on one of its missiles.
On Wednesday Trump tweeted the USA nuclear arsenal was "stronger and more powerful than ever before" but he hoped it never needed to be used.
"North Korea best not make any more threats to the United States".
The official said the threats would only increase as the U.S., South Korea and several allies prepare for joint military exercises on the peninsula beginning August 21.
A senior administration official who deals with the Korea issue said the "fire and fury" comment, which was Trump's strongest warning yet for North Korea and which he delivered to reporters in New Jersey, was "unplanned and spontaneous".
The South Korean capital, Seoul, is within range of massed North Korean rockets and artillery, which would be impossible to destroy in a first U.S. strike.