After pushing for the U.S. to “greatly strengthen and expand” its nuclear capability, President-elect Donald Trump reportedly seemed to welcome an “arms race” in a brief conversation with MSNBC’s Mika Brzezinski Friday morning.

“Let it be an arms race,” he said Friday, according to Brzezinski, co-host of the network’s show Morning Joe.

Brzezinski reported that the president-elect had told her in a telephone call that took place off camera during a commercial break, “We will outmatch them at every pass... and outlast them all.”

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The comments to MSNBC came after transition aides to the president-elect spoke less about the potential expansion of U.S. nuclear arsenal and more about the actions of other countries.

Sean Spicer, Mr. Trump’s newly-named White House press secretary, told MSNBC Friday that “the president-elect’s point is unless these guys come to their senses and recognize that this is not a smart move, increasing the nuclear stockpile around the globe is not good for anybody. But the U.S. is not going to sit back.”

Asked whether Mr. Trump’s tweet was a response to Vladimir Putin, who had also called for ramping up Russia’s nuclear capabilities earlier this week, Spicer said: “I think it’s putting every nation on notice that the United States is going to reassert its position in the globe.”

Spicer denied, however, that it was a direct response to the Russian leader: “It’s not a reaction -- it’s a point that he’s making which is domestically and internationally, business as usual is over.”

On Friday, the Trump transition team also released a letter Putin had sent to “His Excellency Donald Trump,” dated Dec. 15, 2016. In the transition’s statement, Mr. Trump called it “a very nice letter from Vladimir Putin.”

“His thoughts are so correct,” he said. “I hope both sides are able to live up to these thoughts, and we do not have to travel an alternate path.”

The letter from Putin, who likely approved Kremlin-directed cyber attacks affecting the U.S. election, extended his “warmest Christmas and New Year greetings” and discussed relations between the two countries in broad terms.

“Serious global and regional challenges, which our countries have to face in recent years, show that the relations between Russia and the U.S. remain an important factor in ensuring stability and security of the modern world,” Putin wrote. “I hope that after you assume the position of the President of the United States of America we will be able – by acting in a constructive and pragmatic manner - to take real steps to restore the framework of bilateral cooperation in different areas as well as bring our level of collaboration on the international scene to a qualitatively new level.”