President-elect Donald Trump wants the United States to "greatly strengthen and expand" its nuclear capability.
In a tweet, he appeared to suggest he wants America to continue in its perceived role as the world's police force.
He tweeted: "Must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes."
His comments come just hours after Russian President Vladimir Putin called for his country to "strengthen the military potential of its nuclear forces".
Mr Putin 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."
Mr Trump has been meeting top military advisers to discuss defence budgets.
A spokesman for Mr Trump has said his tweet was referring to the need to prevent nuclear proliferation.
During the presidential campaign, defeated Democratic candidate Hillary Clinton repeatedly claimed the Republican was too erratic and unpredictable to have control of the country's nuclear arsenal.
Ten former nuclear missile launch operators also wrote that Mr Trump lacked the temperament, judgement and diplomatic skill to avoid nuclear war.
In March, Mr Trump suggested the world would be "better off" if other countries, including Japan and South Korea, had nuclear capabilities.
He said: "It's going to happen anyway. It's only a question of time. They're going to start having them, or we have to get rid of them entirely."
The Republican also said he "hated" nuclear proliferation "more than any".
Mr Trump was then asked by an interviewer: "So, you're saying you don't want more nuclear weapons in the world, but you're okay with Japan and South Korea having nuclear weapons?"
The tycoon responded: "I don't want more nuclear weapons", adding: "We can't afford it anymore."
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