 -- President Donald Trump on Thursday renewed his call to expand the country's nuclear weapons cache so that the U.S. is the "top of the pack," according to an interview with Reuters.

Trump's comments echoed statements he offered in December when he tweeted about "expand[ing]" the nation's "nuclear capability" and told MSNBC that he was willing to engage in an "arms race."

Trump told Reuters today he wants the country's cache of weapons to be "top of the pack," a notion expanded upon by White House Press Secretary Sean Spicer at his daily press briefing.

"The U.S. will not yield its supremacy in this area to anybody," said Spicer. "That’s what he made very clear [during the interview], and that if other countries have nuclear capabilities, it’ll always be the United States that [has] the supremacy and commitment to this."

On Dec. 22, Trump -- who indicated during the campaign that some nuclear proliferation might be good -- advocated in a tweet for bolstering American capabilities.

The next day, speaking by phone to Mika Brzezinski, the co-host of MSNBC's "Morning Joe," Trump said he'd be open to competing with other countries to accumulate weapons.

“Let it be an arms race,” said Trump. “We will outmatch them at every pass and outlast them all.”

In Thursday's Reuters interview, Trump brought up both Russian cruise missile usage and North Korean missile tests and told the news outlet that the U.S. "has fallen behind in its atomic weapons capacity."

The U.S. has a total of 4,571 warheads in its functional stockpile, a State Department official said. Of those, 1,367 are deployed, while Russia has 1,796 deployed. Both countries have until 2018 under the 2011 New START agreement to limit deployed nuclear weapons to 1,550.

The Pentagon has begun a modernization of the American nuclear program which former Defense Secretary Ash Carter said earlier this year will cost $350 - $450 billion to update beginning in 2021.