President Donald Trump boarding Air Force One on Friday for travel to New Jersey from Joint Base Andrews in Maryland. REUTERS/Jonathan Ernst

President Donald Trump praised the US nuclear arsenal in a series of tweets Wednesday morning, a day after he threatened North Korea with "fire and fury."

"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.

Trump ordered a review of the US's nuclear posture, during which little changes with the weapons themselves as experts evaluate them. During Trump's time in office, the US has carried out three tests of Minuteman III intercontinental ballistic missiles, but those had been scheduled for tests during the Obama administration.

Trump's plans to modernize the US's nuclear arsenal, which the Pentagon deemed in 2013 one-third larger than necessary, remain unchanged from Obama-era proposals.

The president addressed growing tensions between the US and North Korea during a statement Tuesday from his private club in Bedminster, New Jersey.

"He has been very threatening beyond a normal state," Trump said of Kim Jong Un, North Korea's leader. "As I said, they will be met with fire, fury, and frankly power, the likes of which this world has never seen before."

North Korea responded Tuesday by threatening a missile strike on Guam.

Secretary of State Rex Tillerson urged calm Wednesday morning, saying he didn't think there was "any imminent threat" from North Korea.

Tillerson said Trump was trying to send a strong and clear message to North Korea's leader so that there wouldn't be "any miscalculation."

"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," Tillerson 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."

The Associated Press contributed reporting to this story.