"It is a situation that we will handle," he added, in remarks designed to show resolve, but which offered little clue of an immediate US response.

 The US president has threatened North Korea with "fire and fury" if it continues to work toward an ICBM capable of carrying a nuclear payload.

 A more than two-month pause in tests had prompted speculation about whether North Korea might be willing to embrace a negotiated solution to the nuclear standoff.

 Shortly after Trump spoke, Secretary of State Rex Tillerson said "diplomatic options remain viable and open" on North Korea -- but they now appear to be further away than ever before.

 Mattis said South Korea had responded to the test by launching pinpoint missile strikes into the water -- an effort to show North Korea that a true attack would bring a swift and crippling response. 

 Since coming to office, Trump has ratcheted up the diplomatic and economic pressure on the regime of Kim Jong-Un.

 He has pressed China to break trade ties with its dependent neighbor and has applauded countries for shuttering Pyongyang's diplomatic installations, which have long been used to gather illicit finance.

 Earlier this month, Trump declared North Korea a state sponsor of terrorism

-- a symbolic move, but one which amps up diplomatic pressure on the regime.

 "We have a very serious approach. Nothing changed," Trump said.