President Trump reportedly told national security leaders in July he wanted to increase the U.S. nuclear arsenal by tenfold, which prompted Secretary of State Rex Tillerson to call the president "a moron."

In a July meeting, Trump said he wanted more nuclear weapons when he was shown a briefing slide of the U.S. and Russia's nuclear capabilities, NBC News reported Wednesday. The chart showed the U.S. arsenal was at its peak in the late 1960s.

Officials present at the Pentagon meeting told the news outlet that Trump's advisers and Tillerson were surprised by the request. Officials explained to the president the legal and practical ramifications of such actions.

It was after the July 20 meeting ended that officials heard Tillerson called Trump "a moron," which has been disputed by the State Department and the president himself.

Nonproliferation experts told NBC that a move by the U.S. to increase its nuclear weapons could set off an arms race. It also would break treaties signed by every U.S. president since Ronald Reagan.

News of Trump's comments come amid a standoff between the U.S. and North Korea over the latter's efforts to obtain a nuclear weapon. Trump also faces a Sunday deadline to recertify the Iran nuclear deal, which he has hinted will not happen.

Some officials in the meeting said they were unnerved by Trump's comments and his understanding of other national security issues.

Trump also expressed a desire for more U.S. troops and military equipment.

Vice President Pence, Treasury Steven Mnuchin, Defense Secretary James Mattis, Chairman of the Joint Chiefs General Joseph Dunford, former chief strategist Stephen Bannon, senior adviser Jared Kushner and former chief of staff Reince Priebus also attended the meeting.