A spokesman for Donald Trump says the US President-elect's statement that the United States needs to strengthen its nuclear capabilities referred to the need to prevent nuclear weapons from spreading to unstable countries or terrorist groups.
"President-elect 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," spokesman Jason Miller said on Thursday.
In his Twitter post earlier, Trump wrote: "The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes."
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 $US1 trillion ($A1.4 trillion) over 30 years, according to independent estimates.
Trump, who is at his Florida resort for the Christmas holiday, gave no details about what prompted his tweet.
Trump, who won election on November 8 and takes office on January 20, campaigned on a platform of building up the US military, but also pledged to cut taxes and control federal spending.
Trump met on Wednesday with a dozen Pentagon officials involved with defence acquisition programs, as well as the chief executives of Lockheed Martin Corp and Boeing Co, the country's two largest defence contractors.
Trump said he talked with the CEOs about lowering costs for two high-profile programs: Lockheed Martin's F-35 fighter jets and Boeing's replacement 747-8s for the presidential Air Force One plane.
Defence stocks were little changed after Trump's tweet, but shares of small uranium miners including Uranium Resources Inc and Uranium Energy Corp rose sharply.