President Donald Trump warned the world on Monday that the United States intended to expand its nuclear arsenal if Russia and China continued to build up their own stockpiles.
Speaking to reporters at the White House before leaving for a campaign rally in Nevada, Mr Trump repeated his accusation that Russia is violating the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, which he wants to abandon.
Russia denies the allegation but Mr Trump insisted the US would press ahead with developing its own stockpile.
"Until people come to their senses, we will build it up," he said.
Washington has long accused Russia of violating the INF Treaty, which was signed by Ronald Reagan and Mikhail Gorbachev, helping end a crisis that began with the deployment of Soviet SS-20 nuclear missiles aimed at Western capitals.
American officials also say it puts the US at a disadvantage to China, which is not a signatory.
Mr Trump continued: "It's a threat to whoever you want. And it includes China and it includes Russia and it includes anybody else that wants to play that game."
The president's national security adviser, John Bolton, is in Moscow for talks.
His arrival was preceded by a wave of Russian anger at Mr Trump's plan to withdrawal.
On Monday, officials said they would work to maintain a balance of power if the US pulled out.
Dmitry Peskov, Kremlin spokesman, said: "It means that the United States is not disguising, but is openly starting to develop these systems in the future, and if these systems are being developed, then actions are necessary from other countries, in this case Russia, to restore balance in this sphere."
A day earlier, Mr Gorbachev expressed fears that US withdrawal would reverse years of progress in disarmament.