Hours after President Trump announced that the U.S. will pull out of a decades-old bilateral nuclear agreement that he said Russia had been "violating for many years," top Russian officials lined up to hit back in no uncertain terms, calling the president's move a "very dangerous" provocation that would lead to "full chaos."

"We condemn the ongoing attempts by blackmail to achieve concessions from Russia," Russian Deputy Foreign Minister Sergei Ryabkov told a state news agency. "This would be a very dangerous step."

Konstatin Kosachev, who chairs the foreign affairs committee in the Federation Council, Russia's upper house of parliament, wrote on Facebook that Trump's decision meant "mankind is facing full chaos in the nuclear weapons sphere."

And prominent Russian senator Aleksey Pushkov charged that Trump's move meant "United States is bringing the world back to the Cold War," saying the U.S.' withdrawal from the treaty would be a "massive blow to the entire system of strategic stability in the world." Pushkov had previously criticized claims that Russia meddled in the 2016 U.S. presidential election, arguing those suggestions are part of a plan to continue a "new Cold War."

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The 1987 Intermediate Range Nuclear Forces (INF) treaty ostensibly prevents both the United States and Russia from possessing, producing or test-flying any ground-launched cruise missile with a range of 300 to 3,400 miles. President Ronald Reagan and General Secretary Mikhail Gorbachev inked the deal because of an unfolding crisis.

"We’re not going to let them violate a nuclear agreement." — President Trump

But the Trump administration has said Russia broke the deal by deploying Novator 9M729 land-based cruise missiles, which can exceed that range and strike NATO countries quickly. The U.S. has previously acknowledged that Russia was violating the treaty in 2012 under the Obama administration, and for their part, Russian officials have also suggested the U.S. hasn't complied with the treaty by placing missiles in European bases.

After speaking at a campaign rally in Elko, Nevada, on Saturday, Trump said the agreement did little more than interfere with U.S. military development.

"We’re going to terminate the agreement, and we’re going to pull out,” Trump told reporters. "They have been violating it for many years. I don't know why President [Barack] Obama didn't negotiate or pull out. ... We’re not going to let them violate a nuclear agreement and go out and do weapons, and we’re not allowed to."

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NATO Secretary General Jens Stoltenberg concurred with Trump's assessment earlier this month. (The Defense Department concluded in February that Russia was actively violating its arms treaty agreements, as well.)

"This treaty abolishes a whole category of weapons and is a crucial element of our security. Now this treaty is in danger because of Russia's actions," Stoltenberg said. "After years of denials, Russia recently acknowledged the existence of a new missile system, called 9M729. Russia has not provided any credible answers on this new missile. All allies agree that the most plausible assessment would be that Russia is in violation of the treaty. It is therefore urgent that Russia addresses these concerns in a substantial and transparent manner."

On Saturday, Trump went on to say he would be open to a new, similar agreement only if Russia and China signed on and demonstrated a sincere commitment.

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

UK Defense Secretary Gavin Williamson forcefully backed the U.S. in an interview with The Financial Times, saying that Russia had made a "mockery" of the agreement.

“Our close and long-term ally, of course, is the United States and we will be absolutely resolute with the United States in hammering home a clear message that Russia needs to respect the treaty obligation that it signed," Williamson said.

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But Sen. Rand Paul, R-Ky., who sits on the Senate Foreign Relations Committee, called Trump's pullout a "big, big mistake" on "Fox News Sunday," echoing comments he made Saturday on Twitter.

Trump's announcement comes as National Security Adviser John Bolton makes his way to Moscow on Monday and Tuesday, before a trip to countries elsewhere in the region. Bolton is expected to discuss a range of issues with his Russian counterparts, including Russia's deployment of a S-300 missile defense system in Syria, the recent poisoning of a former Russian spy in Britian, and the nuclear accord.

Also expected to headline discussions are renegotiations of the New Strategic Arms Reduction Treaty (START), which is slated to expire in 2021. Signed by Obama and former Russian president Dmitri Medvedev, the deal limits the number of strategic warheads both countries are allowed to deploy.

Trump and Putin are expected to attend another high-level summit, following their widely-criticized meeting in Helsinki, Finland in July. Critics charged Trump was too ready to accept Putin's denials of any meddling in U.S. elections.

"This is the most severe crisis in nuclear arms control since the 1980s,” Malcolm Chalmers, the deputy director general of the Royal United Services Institute, said in an interview. “If the INF treaty collapses, and with the New Start treaty on strategic arms due to expire in 2021, the world could be left without any limits on the nuclear arsenals of nuclear states for the first time since 1972.”