President Donald Trump denied a report on Wednesday that he previously asked for a tenfold increase to the U.S. nuclear arms supply.

NBC News published a piece alleging that he made the request over the summer after seeing a slide displaying the reduction in American nuclear weaponry since the 1960s.

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! — Donald J. Trump (@realDonaldTrump) October 11, 2017

“According to the officials present, Trump’s advisers, among them the Joint Chiefs of Staff and Secretary of State Rex Tillerson, were surprised,” the NBC piece says. “Officials briefly explained the legal and practical impediments to a nuclear buildup and how the current military posture is stronger than it was at the height of the buildup. In interviews, they told NBC News that no such expansion is planned.”

Secretary of Defense Jim Mattis on Wednesday called the reports “absolutely false.”

“Recent reports that the president called for an increase in the U.S. nuclear arsenal are absolutely false. This kind of erroneous reporting is irresponsible,” Mattis said in a statement.

Trump also threatened NBC that he would “challenge their license,” although what that would entail specifically is unclear. The Federal Communications Commission, the body that oversees licensing, didn’t immediately respond to a request for comment, but its website notes that it doesn’t oversee television or radio networks.

Trump’s tirade against the network ramped up last week after NBC reporters nabbed a scoop claiming that Tillerson called him a “moron” and threatened to not return to Washington, D.C., while he was visiting Texas.

Wow, so many Fake News stories today. No matter what I do or say, they will not write or speak truth. The Fake News Media is out of control! — Donald J. Trump (@realDonaldTrump) October 4, 2017

NBC news is #FakeNews and more dishonest than even CNN. They are a disgrace to good reporting. No wonder their news ratings are way down! — Donald J. Trump (@realDonaldTrump) October 4, 2017

The @NBCNews story has just been totally refuted by Sec. Tillerson and @VP Pence. It is #FakeNews. They should issue an apology to AMERICA! — Donald J. Trump (@realDonaldTrump) October 4, 2017

Tillerson ended up making on-camera remarks the same day following rumors that the piece was an indication that he planned to resign. He didn’t deny having made the comment but did brush off the rumor as “petty stuff.” He also reaffirmed his commitment to Trump and to the country.

Trump attacked NBC several more times over the course of the week, insisting that Tillerson never threatened to resign. NBC told HuffPost last week in a statement that it stood by its reporting.

This article has been updated with information about the Federal Communications Commission and comment from Jim Mattis.