"The DPRK must choose to stop isolating itself and stand down its pursuit of nuclear weapons", Mattis said in a statement.
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".
North Korean said it was considering plans for a missile strike on the US Pacific territory of Guam, after Trump on Tuesday said any North Korean threat to the United States would be met with "fire and fury".
It comes following an exchange of threats and boasts of nuclear power by President Donald Trump and North Korea. "They will be met with fire and fury like the world has never seen".
"While our State Department is making every effort to resolve this global threat through diplomatic means, it must be noted that the combined allied militaries now possess the most precise, rehearsed and robust defensive and offensive capabilities on Earth", he said in a statement.
Nelson says he's anxious North Korea's ability to put a nuclear device on a long-range missile will only embolden dictator Kim Jong-Un.
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The ASEAN ministers also noted concerns expressed by some members about land reclamations and noted "the importance of non-militarization".
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Dianne Feinstein, D-Calif., also was critical of the president's comments. "Today is truly a sad day indeed", he said. It is about 2,200 miles (3,500 km) southeast of North Korea, much closer than it is to any of the United States.
Bill Nelson, Florida's senior U.S. Senator, says he's deeply concerned about North Korea's ability to arm an ICBM with a nuclear warhead.
Congressman Dan Kildee of MI was in South Korea wehn the North Korean regime tested another missile.
Tillerson has maintained that the USA is open to dialogue with North Korea, if it promises to abandon its development of nuclear weapons. "It is now far stronger and more powerful than ever before", Trump wrote.
Mattis has warned that North Korea now poses the most urgent threat to United States peace and security, but also that any war with Pyongyang would include "probably the worst kind of fighting in most people's lifetime", citing the threat posed by hundreds of North Korean rocket launchers and artillery pieces aimed at Seoul. Before Trump's tweets on the nuclear arsenal, Tillerson arrived in Guam on a previously scheduled visit after telling reporters he did not believe there was an imminent threat from North Korea and "Americans should sleep well at night".
Secretary of Defense James "Mad Dog" Mattis echoed his boss's fiery warning Wednesday to the dictator of North Korea with harsh rhetoric of his own.
The US, which protects its air and naval bases on Guam with advanced missile defenses, appeared prepared to meet the challenge of North Korea's unreliable missiles.