An LGM-30 Minuteman III intercontinental ballistic missile being serviced in a silo. Department of Defense via Federation of American Scientists President Donald Trump wasn't happy with the steady decrease in the US stockpile of nuclear weapons since the 1960s.

So, over the summer, he asked instead for a tenfold increase in the US's nuclear weapons, NBC News reported on Wednesday, adding that the request startled his advisers and was followed soon after with Secretary of State Rex Tillerson calling him a "moron."

Trump on Wednesday morning called the story "pure fiction, made up to demean."

"Fake @NBCNews made up a story that I wanted a "tenfold" increase in our U.S. nuclear arsenal. Pure fiction, made up to demean. NBC = CNN!" Trump tweeted.

Upon seeing a briefing that charted the huge decline in the number of US nuclear weapons, NBC News said, citing three anonymous officials, Trump asked the military officials present to expand the arsenal to nearly 10 times its current size.

It was soon after this meeting that NBC News' sources heard Tillerson call Trump a moron, sparking a news story that would eventually require Tillerson to respond in an impromptu news conference and Trump to challenge Tillerson to compare IQs.

"I think it's fake news," Trump said of the reported "moron" quip in an interview with Forbes. "But if he did that, I guess we'll have to compare IQ tests."

"And I can tell you who is going to win," Trump said.

NBC News last week reported that Tillerson called Trump the name over the summer after a meeting about Afghanistan in which Trump compared "the decision-making process on troop levels to the renovation of a high-end New York restaurant." Hours after that report, which did not mention the nuclear discussion, Tillerson held a special press conference in which he said, among other things, that Trump "is smart."

Arms-control experts maintain that an increase in US arms would bring about another arms race with Russia and most likely China and could spur other countries to seek nuclear capabilities.

Additionally, they maintain that the US's arsenal is stronger and safer than ever before because of technological improvements since the 1960s, when the stockpile peaked.

But Trump has ordered the Pentagon to review its nuclear posture, with the US reassessing its nuclear assets in light of evolving threats. The most recent nuclear-posture review came in 2010 under President Barack Obama, and it had the express goal of reducing weapons stockpiles.

The US nuclear stockpile over time. Arms Control Association

Preliminary reports indicate that the Trump administration is considering creating smaller, potentially "more usable" nuclear weapons.

Trump has repeatedly expressed a desire to "greatly strengthen and expand [US] nuclear capability." The US is facing a potential trillion-dollar modernization effort to update all three legs of its nuclear triad.

The US's main nuclear rival, Russia, has created newer and in some ways more advanced nuclear weapons and tested them recently.

Throughout his political career, Trump toyed with the idea of allowing South Korea and Japan to build nuclear weapons, and he has flirted with possible nuclear war with North Korea.