Speaking to reporters in Mountain View, California, Mattis said that US efforts on North Korea were now focused on diplomacy, while stressing that his "mission" was to make sure Washington "is to have military options should they be needed".
PRESIDENT DONALD TRUMP: And if he utters one threat in the form of an overt threat, which, by the way, he has been uttering for years and his family has been uttering for years - or if he does anything with respect to Guam or any place else that's an American territory or an American ally, he will truly regret it.
But the tension continued Friday when North Korea said Trump was "driving the situation on the Korean peninsula to the brink of a nuclear war" with his continued rhetoric. But when asked how he would gauge the threat from North Korea, the Secretary said it is "a threat to world peace and global order" and that the human toll from such an attack would be "catastrophic".
A new report says Pyongyang's nuclear program is progressing.
He warned that the tragedy of war is well known and a military conflict could be 'catastrophic'.
United Nations spokesman Stephane Dujarric says Guterres "welcomes all initiatives that will help de-escalate the tensions and a return to diplomacy".More news: Weekend tropical outlook: A depression could develop in the Atlantic
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"If North Korea does anything in terms of even thinking about attack, of anybody that we love or we represent or our allies or us, they can be very, very nervous", Trump said.
"The UK stands shoulder to shoulder with the U.S.in tackling this threat and many others". Trump is issuing a new warning over the North's development of nuclear weapons.
Pyongyang on Thursday announced it was finalising a plan to fire four missiles near the United States territory of Guam.
In a lengthy exchange with reporters at his Bedminster golf resort, he said past administrations had not done enough to take on North Korea and that it was time a president "stuck up for the country". And despite Trump's public bluster, the USA has reportedly been carrying on quiet, back-channel negotiations with North Korea through that country's United Nations representatives.
Japan and South Korea vowed a strong reaction if the North were to go through with the plan.