Trump's advisers were reportedly taken by surprise at his threats to North Korea

AP Photo/Alex Brandon

President Donald Trump.

When President Donald Trump said on Tuesday that North Korea would be met with "fire and fury like the world has never seen" if it continued its nuclear threats, his advisers were taken by surprise, according to a New York Times report on Wednesday.

Trump delivered the threat with his arms folded and while looking directly at the camera, and several people with knowledge of the situation told the Times that Trump had not run the language of his statement by any of his advisers beforehand, including Secretary of State Rex Tillerson and chief of staff John Kelly.

Trump's fiery statement followed a Washington Post report that said US intelligence had acknowledged that North Korea could make nuclear warheads small enough to fit on missiles and that the country may have as many as 60 nuclear devices.

Trump's statement represented a marked escalation in tensions between the two countries, and North Korea retaliated by threatening to strike a US air base in Guam.

Since Tuesday's events, Trump's advisers have reportedly sought to diffuse the heated situation, and Tillerson said Americans "should sleep at night" without worrying about the threat of a nuclear war.

On Wednesday, Trump appeared to attempt and assuage further concerns by touting the US' nuclear arsenal's strength on Twitter.

"My first order as President was to renovate and modernize our nuclear arsenal. It is now far stronger and more powerful than ever before," Trump tweeted.

"Hopefully we will never have to use this power, but there will never be a time that we are not the most powerful nation in the world!" he added.

Despite those comments, however, "nothing has changed on the ground in the last six months" with the US's nuclear weapons systems, Daryl Kimball, the executive director of the Arms Control Association, told Business Insider earlier on Wednesday.

Alex Lockie contributed to this report.