The official, in an exclusive interview to The Associated Press, said that if the US shows any sign of "reckless" military aggression, Pyongyang is ready to launch a pre- emptive strike of its own.
Vice Minister Han Song Ryol said Pyongyang has determined the Trump administration is "more vicious and more aggressive" than that of Barack Obama. He added that North Korea will keep building up its nuclear arsenal in "quality and quantity" and said Pyongyang is ready to go to war if that's what Trump wants.
This year's joint war games between the US and South Korean militaries are the biggest so far the USS Carl Vinson aircraft carrier has been diverted back to the waters off Korea after heading for Australia, and US satellite imagery suggests the North could conduct another underground nuclear test at any time.
Pyongyang recently tested a ballistic missile and claims it is close to perfecting an intercontinental ballistic missile and nuclear warhead that could attack the US mainland.
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"That is something that our headquarters decides," he said during the 40-minute interview in Pyongyang, which is now gearing up for a major holiday and possibly a big military parade tomorrow. "At a time and at a place where the headquarters deems necessary, it will take place."
The annual US-South Korea military exercises have consistently infuriated the North, which views them as rehearsals for an invasion. Washington and Seoul deny that, but reports that exercises have included "decapitation strikes" aimed at the North's leadership have fanned Pyongyang's anger.
Han said Trump's tweets have also added fuel to the flames.
Trump posted a tweet Tuesday in which he said the North is "looking for trouble" and reiterated his call for more pressure from Beijing, North Korea's economic lifeline, to clamp down on trade and strengthen its enforcement of UN sanctions to persuade Pyongyang to denuclearise.
"Trump is always making provocations with his aggressive words," Han said. "It's not the DPRK but the US and Trump that makes trouble." North Korea's official name is the Democratic People's Republic of Korea.