In a tweet, Trump appeared to suggest the US should enlarge its arsenal in response to other nations’ nuclear programmes.
The President Elect wrote: “The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes.”
The missive provoked a fierce response on social media in the US and the UK. “Well, we’ve had a good run,” actor Mark Gatiss wrote.
A spokesperson for Trump later said the tweet was referring to the need to prevent nuclear proliferation.
Trump’s tweet came just hours after Russian President Vladimir Putin called for the country to reinforce its military nuclear potential.
Speaking to mark his military’s achievements in 2016, Putin said the army’s preparedness has “considerably increased” and called for continued improvement that would ensure it can “neutralise any military threat”.
“We need to strengthen the military potential of strategic nuclear forces, especially with missile complexes that can reliably penetrate any existing and prospective missile defence systems,” Putin said.
He added: “We must carefully monitor any changes in the balance of power and in the political-military situation in the world, especially along Russian borders, and quickly adapt plans for neutralising threats to our country.”
Trump’s startling words come after a day of meetings with military officials to discuss the defence budgets.
Attendees to Trump’s estate near Palm Beach, Florida, included Lieutenant General Jack Weinstein, deputy chief of staff for strategic deterrence and nuclear integration for the US Air Force.
And his comments came one day after meeting with incoming White House national security adviser Michael Flynn, the Associated Press reported.
But Thursday’s declaration represents a departure for Trump who had previously told CNN’s Anderson Cooper: “I don’t want more nuclear weapons”, adding: “We can’t afford it anymore.”
The Ploughshares Fund, a global security foundation, has estimated there are more than 15,000 nuclear weapons around the world.
The US and Russia possess 93 percent of them.
Hillary Clinton, Trump’s failed opponent, repeatedly cast the Republican as too erratic and unpredictable to have control of America’s nuclear arsenal.
And former nuclear missile launch operators also wrote that Trump lacks the temperament, judgment and diplomatic skill to avoid nuclear war.
In March, Trump refused to rule out dropping a nuclear weapon on Europe.
In a Town Hall interview with MSNBC’s Chris Matthews, the then candidate said he would be “the last one to use nuclear weapons”.
But when asked whether he would attack Europe or the Middle East with nukes if he felt it necessary, Trump said he was “not going to take it off the table”.
Matthews: “You might in Europe?”
Trump: “No. I don’t think so.”
Matthews: “Well just say it: ‘I will never use a nuclear weapon in Europe.’”
Trump: “I am not taking cards of the table. I’m not going not use nukes. But I’m not taking any cards of the table.”
At the time, Clinton said she did not think Trump “even studies or cares to understand” foreign policy.
Reaction to Trump’s tweet was perhaps predictably bleak. Many people highlighted the timing of his declaration.
GMB presenter Piers Morgan asked: “What’s more dangerous - Trump wanting to strengthen US nuclear deterrent, or [Jeremy] Corbyn saying he’d never use ours?”