Speaking at an event in California on Thursday, Mattis said his mission and responsibility was to have military options ready "should they be needed" but stressed the United States effort is now focused on diplomacy.
"The tragedy of war is well enough known", Mattis said, responding to a question about the human toll of a nuclear confrontation between the DPRK and the U.S.
He spoke a day after President Trump warned that he would unleash "fire and fury like the world has never seen" if North Korea continued to threaten America, rhetoric that suggested the two countries are edging closer to conflict.
North Korea talk drags stocks lower; gold, yen rise
In commodities, US. crude fell 0.67 per cent to $49.23 per barrel and Brent was last at $52.58, down 0.23 per cent on the day. An index of 15 gold miners tracked by Bloomberg Intelligence climbed 1.1 percent, led by Toronto-based Yamana Gold Inc.
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"No Easy Military Options in North Korea" is part of Aviation Week & Space Technology's subscription package. North Korea says it will "keep closely watching the speech and behavior of the U.S".
North Korea successfully tested an intercontinental ballistic missile last month for the first time, and US intelligence agencies assess that Pyongyang is capable of producing a compact nuclear warhead and putting it atop a long-range missile.
"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely".
Arsene Wenger on Alexis Sanchez signing Arsenal deal
He missed the Community Shield victory over Chelsea with flu and now Wenger has said he is out with an abdominal strain. But manager Arsene Wenger is still uncertain as to whether the salary increase will be enough to extend Sanchez's deal.
Secretary of State Rex Tillerson has urged calm, saying he sees no "imminent threat" of attack.
A number of USA allies, including Australia and Japan, have said that they're prepared to stand with Trump and will take military action against North Korea if Jong Un launches an attack against Guam, according to Fox News. Mattis said that this show of support is heartening.
North Korea Has Markets Nervous But Not Panicked
Japan is the world's biggest creditor country and there is an assumption investors there will repatriate funds in a crisis. The Nasdaq Composite Index plunged 2.1% to 6216.87 and the Standard & Poor's 500 Index dropped 1.45% to 2438.21.
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