Story highlights "The tone and strength of the message were discussed beforehand," Sanders said

Trump has long been bothered by North Korean Leader Kim Jong Un's threats

Bridgewater, New Jersey (CNN) President Trump's fierce warning to North Korea was improvised in the moment, not part of a scripted statement that he prepared to deliver Tuesday, according to three people with knowledge of the remarks.

Trump has long been bothered by North Korean Leader Kim Jong Un's threats against the United States and has privately vented about a powerful United States response to the rogue nation. His statement on Tuesday, flanked by top White House aides and his new chief of staff Gen. John Kelly, mimics those private remarks, a source said.

"North Korea best not make any more threats to the United States," Trump said during a meeting on opioids from his golf club in New Jersey. "They will be met with fire and fury like the world has never seen ... he has been very threatening beyond a normal state. They will be met with fire, fury and frankly power the likes of which this world has never seen before."

Trump's comment, which came shortly before North Korean officials threatened the United States territory of Guam with missiles, was criticized as too bellicose and direct by national security and defense experts who argued any conflict involving nuclear weapons called for calm and reserve.

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