Asked if he thought North Korean leader Kim Jong Un was a rational actor, Mattis said he would leave it to those seeking the answer to figure out themselves.
Though not a direct response to the "fire and fury" statement, North Korea's army announced hours after that it was preparing a plan for missile strike on the USA territory of Guam should Washington carry out military action against the DPRK.
One U.S. military official speaking to NBC spoke of the concern that a pre-emptive attack against the DPRK would result in a response, putting people in South Korea at potential risk.
U.S. Defense Secretary General James Mattis said on Thursday that the country's military is "ready" to counter the threat from North Korea.
North Koreans holding national flags march during a parade to mark the 60th anniversary of the signing of a truce in the 1950-1953 Korean War at Kim Il-sung Square, in Pyongyang July 27, 2013.
'But of course if North Korea decides to carry out some of its violent threats, then obviously bad consequences will follow, and there's no point ducking that inevitable effect, ' he said, promising Australian military support for the United States if it was attacked.
The aircraft carrier USS Carl Vinson transits the South China Sea while conducting flight operations on April 9, 2017.
South Korea's national security adviser Chung Eui-yong and his US counterpart H.R. McMaster spoke on the phone for 40 minutes early on Friday, a spokesman for the presidential Blue House in Seoul said. He said the US nuclear arsenal is the most powerful it's ever been under his leadership.
'The current situation on the Korean Peninsula is highly complicated and sensitive.
The president's public comments "undermine anyone in Pyongyang who's interested in seeing if there's something to be gained in a dialogue with the United States", he said.
"I was not elected, the American people elected the president", he said.