Vermont Senator Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I) dubbed President-elect Donald Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE the "Tweeter in Chief" Friday afternoon for potentially sparking an arms race through Twitter.

Sanders's criticism comes a day after Trump tweeted that the United States should "greatly strengthen and expand its nuclear capability," and just hours after Trump reportedly told MSNBC's Mika Brzezinski "let it be an arms race" in an off-air phone call.

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"Congress must not allow the Tweeter in Chief to unleash a dangerous and costly nuclear arms race," Sanders wrote Friday in his response to Trump.

Congress must not allow the Tweeter in Chief to unleash a dangerous and costly nuclear arms race. https://t.co/YYdlo3tSoa — Bernie Sanders (@SenSanders) December 23, 2016

Trump's tweet was followed by a statement from spokesman Jason Miller, who said that Trump “was referring to the threat of nuclear proliferation and the critical need to prevent it—particularly to and among terrorist organizations and unstable and rogue regimes."

“He has also emphasized the need to improve and modernize our deterrent capability as a vital way to pursue peace through strength,” Miller said.

On Thursday, both Trump and Russian officials expressed a desire for more nuclear weapons.

The statements have sparked backlash from politicians and political observers who say the countries are reigniting an arms race reminiscent of the Cold War stand-off between the U.S. and the Soviet Union.