Mr Tillerson sought to downplay the escalating diplomatic crisis, saying Americans “should sleep well at night”.
"I do not believe that there is any imminent threat" from North Korea, he added.
His intervention came after Mr Trump told North Korea’s leadership it would be "met with fire and fury like the world has never seen" if it made more threats to the US.
Pyongyang in turn said it was "carefully examining the operational plan for making an enveloping fire at the areas around Guam", an island in the Pacific home to around 6,000 US military personnel.
Mr Tillerson, speaking as he returned from a tour of Southeast Asia, said the President’s comments were an attempt to prevent “any miscalculation” by the North.
"What the President is doing is sending a strong message to North Korea in language that Kim Jong-un can understand, because he doesn't seem to understand diplomatic language," the Secretary of State said.
"I think the President just wanted to be clear to the North Korean regime on the US’ unquestionable ability to defend itself, will defend itself and its allies."
But he also risked upping the ante as he warned that Guam was not the only place that was at risk from a missile strike.
The plane carrying Mr Tillerson from Malaysia to Washington included a scheduled stop in Guam to refuel.
He said re-routing his trip to avoid stopping in Guam had not been considered as "the North Korean missile capability can point in many directions, so Guam is not the only place that would be under threat”.
Mr Tillerson, who had been in Asia to work on a solution to the crisis, also insisted the Trump administration’s current strategy to deal with Mr Kim was working.
"The pressure is starting to show," he said. "I think that's why the rhetoric coming out of Pyongyang is beginning to become louder and more threatening.
“Whether we've got them backed into a corner or not is difficult to say, but diplomatically, you never like to have someone in a corner without a way for them to get out."
Pressed on whether Pyongyang had a way out, with rhetoric from both sides suggesting they were on course for conflict, Mr Tillerson replied that the option of dialogue remained on the table.
"Talks, with the right expectation of what those talks will be about,” he said.
Mr Tillerson has held the door open for dialogue with North Korea on numerous occasions, including at a security forum in Manila on Monday, when he said: "The best signal that North Korea can give us that they are prepared to talk would be to stop these missile launches.”
Earlier in August, he said he was willing to sit down for talks as long as Mr Kim abandoned his quest to develop nuclear weapons.
Speaking to the regime directly, he said: "We do not seek regime change. We do not seek an accelerated reunification of the peninsula. We do not seek an excuse to send our military north of the 38th parallel.
"We are not your enemy, we are not your threat, but you are presenting an unacceptable threat to us and we have to respond.
"We would like to sit and have a dialogue about the future."
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