"We're so prepared like you wouldn't believe," Trump told the Fox News program Sunday Morning Futures while discussing tensions with North Korea, which have soared over Pyongyang's nuclear program.
"You would be shocked to see how totally prepared we are if we need to be," said Trump, who has in recent months engaged in a fiery verbal tit-for-tat with North Korea's leader.
"Would it be nice not to do that? The answer is yes," Trump went on, appearing to allude to potential conflict.
"Will that happen? Who knows," the US president said.
The North has drawn international ire in recent months for conducting a sixth nuclear test and tests of long-range missiles capable of striking the US mainland.
Asked about US policy towards China, the North's longtime ally, Trump praised Beijing for "helping" the US by enforcing sanctions against Pyongyang.
"He's for China. And I'm for the US," he said of Chinese President Xi Jinping. "But we do have a very good -- I would say an exceptional relationship. And China's really helping us. With respect to North Korea."
"China is big stuff," he added, saying Xi has "got the power to do something very significant with respect to North Korea."
In a separate development, former US president Jimmy Carter told The New York Times he has offered to go to North Korea on behalf of the White House to try to allay rising tensions, though he has not been asked.
The 93-year-old Democrat, who was president from 1977 to 1981, said he had told the Republican president's National Security Advisor HR McMaster that he "was available if they ever need me."
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