President Donald Trump at his New Jersey club in August, 2017. AP Photo/Evan Vucci President Donald Trump tweeted Wednesday that his "first order as President was to renovate and modernize" the US' nuclear arsenal, which "is now far stronger and more powerful than ever before."

The remark came amid increasing tensions with North Korea, which has reportedly developed technology that would allow it to miniaturize nuclear weapons, according to The Washington Post.

Pyongyang threatened to attack Guam after Trump told reporters on Tuesday that further threats from North Korea would be met with "fire and fury like the world has never seen before."

Experts were quick to push back on the president's tweet, saying the US's nuclear arsenal hasn't actually changed much in the six months since Trump took office. In fact, it would be virtually impossible to make substantive changes to the nuclear program in such a short timeframe.

"The US arsenal is the same as it was the day before inauguration," said Daryl Kimball, executive director of the Arms Control Association. "Nothing has changed on the ground in the last six months."

Kimball said the arsenal is actually "larger than it needs to be."

"The Pentagon determined in 2013 that we have a third more nuclear weapons than are necessary for deterrence," he said, which is why the US is in the middle of a Nuclear Posture Review (NPR) — a process “to determine what the role of nuclear weapons in US security strategy should be," according to the Defense Department.

The White House pointed to Trump's signing of a presidential memorandum on January 27, the aim of which is to "rebuild the armed forces." In the memorandum, Trump directed the secretary of defense to initiate a new review.

But there is "more continuity than there is change" during the review, Kimball said, and no official guidance is offered until after the review is complete.

Washington Post reporter Karen Tumulty said on Twitter that it was actually Trump's predecessor, President Barack Obama, who launched a $1-trillion modernization of the nuclear arsenal. The effort will likely span another two decades at minimum, according to the Arms Control Association (ACA).

"The Obama administration requested large increases for nuclear weapons programs at the Defense and Energy Departments to sustain and modernize the arsenal," the association wrote in a recent fact sheet. "As the [Trump] administration conducts its review, which is slated for completion by the end of the year, its first budget request largely continues the Obama administration’s plans."

Stephen Schwartz, an independent nuclear-weapons policy analyst and author of "Atomic Audit: The Costs and Consequences of US Nuclear Weapons Since 1940," tweeted that Trump's claim to have significantly modernized and improved the US' arsenal was "patently absurd."

"Literally nothing has happened in the last 201 days to increase the overall power of the US nuclear arsenal," Schwartz said.

Alex Lockie contributed reporting.