An unclassified intelligence report concluded that Russian President Vladimir Putin ordered an effort to help Trump's electoral chances by discrediting Democrat Hillary Clinton in the 2016 presidential campaign. Photograph: (Reuters)
Expanding our nuclear arsenal will do nothing to prevent...nuclear terrorism. We have more than enough nuclear weapons: US Nuclear expert
President-elect Donald Trump called for an expansion of the United States' nuclear capabilities on Thursday, in a tweet that alarmed nonproliferation experts who said that a boost to the US arsenal could fuel global tensions.
In his Twitter post, Trump said, "The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes," but gave no further details.
The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes— Donald J. Trump (@realDonaldTrump) December 22, 2016
It was not clear what prompted his comment. However, earlier on Thursday, Russian President Vladimir Putin said that Russia needed to "strengthen the military potential of strategic nuclear forces".
Asked about the tweet, Trump spokesman Jason Miller later said Trump was "referring to the threat of nuclear proliferation and the critical need to prevent it - particularly to and among terrorist organisations and unstable and rogue regimes".
Trump, who takes office on January 20, also has "emphasised the need to improve and modernise our deterrent capability as a vital way to pursue peace through strength," spokesman Jason Miller said.
Miller told Reuters that Trump was not advocating the use of nuclear weapons, and said Trump's comments were not meant to be read as a new policy proposal. Interpretation is especially confusing because Trump has criticised media in the past, saying they should take his words "seriously, but not literally".
As critics worry about Trump's links to Russia, his tweet was published within 24 hours of an almost identical message about increasing nuclear capacity put out by Vladimir Putin.
Compare Trump and Putin statements on nukes, both delivered within last 24 hours pic.twitter.com/0RFylUhpe8— Sarah Kendzior (@sarahkendzior) December 22, 2016
Experts wondered whether Trump's brief tweet meant he wanted to breach limits imposed on US strategic weapons and delivery systems by the 2011 New START treaty with Russia - or planned to expand the non-deployed stockpile.
"It is completely irresponsible for the president-elect or the president to make changes to US nuclear policy in 140 characters and without understanding the implications of statements like ‘expand the capacity,’" said Daryl Kimball, the executive director of the Arms Control Association, a leading proponent of arms control based in Washington.
"He must have leaders around the world trying to guess what he means," Kimball said in an interview. "This is bush league."
Putin, who has said that Trump has confirmed to him that he is willing to mend ties between the two countries, also spoke on Thursday of the need to enhance Russia's nuclear arsenal.
"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," he said in a speech in Moscow.
If Trump and Putin both want to expand nuclear weapons, that would effectively end arms control efforts underway since the Nixon administration, said Joe Cirincione, president of Ploughshares Fund, a foundation that works to prevent the spread and use of nuclear weapons.
"This is how arms races begin - with a battle of words," Cirincione said, urging Trump, a real estate mogul, to "make the biggest deal of his life" and negotiate cuts to the nuclear arsenal with Russia.
"Neither side needs to be spending hundreds of billions of dollars on nuclear weapons we don’t need," Cirincione said.
The United States is one of five nuclear weapons states allowed to keep a nuclear arsenal under the Nuclear Non-Proliferation Treaty. The others are Russia, Britain, France and China.
Trump's "farcical" tweet failed to communicate a "rational deterrence policy" and risks fuelling arms race dynamics with Russia and China, said Miles Pomper, Senior Fellow at the Washington-based Center for Nonproliferation Studies.
The United States needs to do more to prevent nuclear weapons from falling into the wrong hands, rather than creating more materials, Pomper told Reuters.
"Expanding our nuclear arsenal will do nothing to prevent nuclear proliferation or prevent nuclear terrorism. We have more than enough nuclear weapons as it is," Pomper said.
Trump, who was elected on November 8, campaigned on a platform of building up the US military but also pledged to cut taxes and control federal spending.
Most of the US arsenal was built between 25 and 62 years ago during the arms race with the former Soviet Union, and has been patched and otherwise refashioned many times to extend its lifespan.
During the next decade, US ballistic missile submarines, bombers, and land-based missiles - the three legs of the nuclear triad - are expected to reach the end of their useful lives.
Maintaining and modernising the arsenal is expected to cost at about $1 trillion over 30 years, according to independent estimates.
Trump's tweet came the day after meeting with a dozen Pentagon officials involved with defence acquisition programs. He also met with the chief executives of Lockheed Martin Corp and Boeing Co, the country's two largest defence contractors, about high-profile projects he said cost too much.
Late on Thursday, Trump said on Twitter that he had asked Boeing to "price-out a comparable F-18 Super Hornet" because of the "tremendous cost and cost overruns of the Lockheed Martin F-35".