WASHINGTON : Former Democratic presidential candidate Bernie Sanders has dubbed President-elect Donald Trump  as the “Tweeter in Chief” 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 TV  “let it be an arms race” in an off-air phone call.

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

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.

Trump’s remarks were an apparent response to comments by Russian President Vladimir Putin, who on Thursday called for reinforcing military nuclear potential in response to NATO’s planned build-up near his country’s borders.

Putin said that Russia’s military was “stronger than any potential aggressor.”

Speaking at a news conference the next day, the Russian president said his earlier comments have been misunderstood in the United States and that he did not regard Washington as a potential aggressor. “Of course the US has more missiles, submarines and aircraft carriers, but what we say is that we are stronger than any aggressor, and this is the case,” he added.

Putin also said that there is nothing new or remarkable in Trump’s statement, because he had been talking about “the necessity of strengthening the US nuclear arsenal,” during the course of his election campaign.

The Russian president said Moscow would never be the one to unleash an arms race. “We will never spend resources on an arms race that we can’t afford.” Trump’s comments have been concerning for non-proliferation experts, who warned that a boost to America’s nuclear arsenal could fuel tensions around the world.  The US along with Russia, Britain, France and China, are the five nuclear weapons countries who are allowed to keep a nuclear arsenal under the Nuclear Non-Proliferation Treaty (NPT). India, Pakistan, and Israel also have nuclear weapons but they have not signed the treaty. In addition, North Korea, which reportedly has a couple of atomic bombs, withdrew from the treaty in 2003.

Meanwhile, noted American philosopher and political scientist Noam Chomsky also said he was “frightened” by Trump’s comments on “strengthening and expanding” US nuclear US capabilities.

Chomsky, professor emeritus at the Massachusetts Institute of Technology (MIT), said Trump’s recent tweet about nuclear weapons was “one of the most frightening things I’ve seen recently.” The scholar has been a vocal critic of the incoming president, comparing his campaign proposals and rhetoric to Nazi Germany.

He also criticized the Russian President Vladimir Putin for his planned nuclear buildup.

The Pentagon wants to replace or modernize its nuclear attack force, which is expected to reach the end of its useful life during the next decade. Experts estimate the programme will cost $1 trillion over the next 30 years.

The modernization plan has come under criticism from opponents of nuclearization, who warn it may prompt a new arms race with Russia and China.

Trump’s comments came hours after Putin said his country’s arsenal should be strengthened.

The US currently has an arsenal of about 7,000 nuclear warheads, second only to Russia, which has a few hundred more.

Washington and Moscow finalized New START (Strategic Arms Reduction Treaty) five years ago. The nuclear arms reduction treaty was signed in 2010. The treaty entered into force in 2011 and is expected to last at least until 2021.