U.S. President Donald Trump says the United States will withdraw from a key Cold War-era arms control treaty with Russia.

Trump made the declaration on October 20 as his national security adviser, John Bolton, flew to Moscow for talks with President Vladimir Putin about the Intermediate-Range Nuclear Forces (INF) treaty and other issues.

Trump also repeated longstanding U.S. accusations that Moscow had violated the agreement.

“We’re going to terminate the agreement and we’re going to pull out,” he told reporters during a campaign stop in Nevada.

"Russia has violated the agreement. They have been violating it for many years," Trump said.

"And we're not going to let them violate a nuclear agreement and go out and do weapons and we're not allowed to."

"We'll have to develop those weapons, unless Russia comes to us and China comes to us and they all come to us and say let's really get smart and let's none of us develop those weapons.

"But if Russia's doing it and if China's doing it, and we're adhering to the agreement, that's unacceptable," he added.

The Kremlin did not immediately comment, although Russian state media quoted a source in the Russian Foreign Ministry as claiming the U.S. motive in pulling out of the treat was its dream of creating a "unipolar world."

The 1987 treaty prohibits the United States and Russia from possessing, producing, or deploying a medium-range, ground-launched cruise missile.

U.S. officials have said Russia had been developing the missile for years and, in 2014, Washington made its accusations public.

The U.S. State Department later said Moscow had begun deploying the weapon.

Asked about the U.S. decision, a senior U.S. administration official speaking on condition of anonymity told RFE/RL that: “Across two administrations, the United States and our allies have attempted to bring Russia back into full and verifiable compliance with INF."

He added: “Despite our objections, Russia continues to produce and field prohibited cruise misses and has ignored calls for transparency.”

Russia, for its part, has repeatedly denied the U.S. accusations and also alleged that some elements of the U.S. missile-defense systems in Europe were in violation of the agreement.

The Guardian and The New York Times reported on October 19 that U.S. officials had begun notifying European allies of the U.S. decision to withdraw. The Times said also that no final decision had been made.

The treaty, signed by U.S. President Ronald Reagan and Soviet leader Mikhail Gorbachev, was the first arms control agreement to eliminate an entire class of missiles.

Trump’s declaration came just days after Putin said Russia would only use its nuclear weapons in response to a nuclear attack on the country, in what some arms control experts said appeared to be an important clarification of Russian doctrine.

Putin’s comments appeared in part to be a response to the new U.S. “nuclear posture review,” a Defense Department planning document that lays out the criteria for when Washington would use nuclear weapons.

The review, released in February, calls for revamping the U.S. arsenal and developing new low-yield atomic weapons.

The document also highlighted a Russian doctrine that experts say has been around since the Cold War but has gained new attention amid the tensions between Moscow and Washington.

Under that doctrine, known as "escalate to de-escalate," Moscow stipulates it would use or threaten to use smaller-yield nuclear weapons in a limited conventional conflict in Europe to compel the United States and NATO to back down.

That was seen by many Western officials as lowering the threshold for when such weapons would be used.