President Donald Trump says his intention to scrap a landmark arms control agreement Russia follows years of violations by Moscow in developing prohibited weapons, and “we’re not going to be the only one to adhere to it.” The Kremlin said the pullout “would be a very dangerous step.”

Britain said it stood “absolutely resolute” with the U.S., while Germany called Trump’s move “regrettable.”

WATCH: Trump says U.S. pulling out of nuclear treaty with Russia

0:32 Trump says U.S. pulling out of nuclear treaty with Russia Trump says U.S. pulling out of nuclear treaty with Russia

Heiko Maas said in a statement Sunday that the three-decades-old Intermediate-Range Nuclear Forces Treaty is “an important pillar of our European security architecture” and Trump’s announcement “raises difficult questions for us and Europe.”

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The 1987 pact prohibits the United States and Russia from possessing, producing or test-flying a ground-launched cruise missile with a range of 300 miles to 3,400 miles.

Maas says Germany has repeatedly urged Moscow to “clear up the serious allegations of breaching the INF treaty, which Russia has so far not done.”

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1:36 Moscow condemns Trump’s plan to exit a Cold War-era nuclear treaty as ‘very dangerous’ Moscow condemns Trump’s plan to exit a Cold War-era nuclear treaty as ‘very dangerous’

He says Germany is urging Washington to “consider the possible consequences” of its decision, including for a US-Russian nuclear disarmament treaty beyond 2021.

The 1987 Intermediate-range Nuclear Forces Treaty helps protect the security of the U.S. and its allies in Europe and the Far East. It bars the United States and Russia from possessing, producing or test-flying a ground-launched cruise missile with a range of 300 miles to 3,400 miles.

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“Russia has violated the agreement. They have been violating it for many years,” Trump said Saturday after a rally in Elko, Nevada. “And we’re not going to let them violate a nuclear agreement and go out and do weapons and we’re not allowed to.”

The agreement has constrained the U.S. from developing new weapons, but America will begin developing them unless Russia and China agree not to possess or develop the weapons, Trump said. China is not a party to the pact.

“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 said.

Trump is sending his national security adviser, John Bolton, to Moscow for meetings with Russian leaders, including Foreign Minister Sergei Lavrov and Security Council Secretary Nikolai Patrushev, and was expected to relay the news about Trump’s decision.

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“This would be a very dangerous step,” Russia’s deputy foreign minister, Sergei Ryabkov, was quoted as telling state news agency Tass on Sunday. He said a U.S. withdrawal “will cause the most serious condemnation from all members of the international community who are committed to security and stability.”

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Germany’s foreign minister, Heiko Maas, said Trump’s move was “regrettable,” the treaty was “an important pillar of our European security architecture” and a pullout “raises difficult questions for us and Europe.” Maas also said Germany has repeatedly urged Moscow to “clear up the serious allegations of breaching the INF treaty, which Russia has so far not done.”

But Britain’s defence secretary, Gavin Williamson, said his country stands “absolutely resolute” with the United States on the treaty dispute.

Williamson blamed Russia for endangering the arms control pact and he called on the Kremlin to “get its house in order.”

Williamson told the Financial Times on Sunday that Moscow had made a “mockery” of the Intermediate-Range Nuclear Forces Treaty.

U.S.-Russia relations already are strained as a result of the Ukrainian crisis, the war in Syria and allegations of Russian meddling in the 2016 presidential race and upcoming U.S. midterm elections.

Trump did not provide details about violations. But in 2017, White House national security officials said Russia had deployed a cruise missile in violation of the treaty. Earlier, the Obama administration accused the Russians of violating the pact by developing and testing a prohibited cruise missile.

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Russia has repeatedly denied that it has violated the treaty and has accused the United States of not being in compliance.

Defence Secretary James Mattis has previously suggested that a Trump administration proposal to add a sea-launched cruise missile to America’s nuclear arsenal could provide the U.S. with leverage to try to persuade Russia to come back in line on the arms treaty.

Russia’s Foreign Ministry said in February that the country would only consider using nuclear weapons in response to an attack involving nuclear or other weapons of mass destruction, or in response to a non-nuclear assault that endangered the survival of the Russian nation.

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An independent Russian political analyst, Dmitry Oreshkin, said, “We are slowly slipping back to the situation of cold war as it was at the end of the Soviet Union, with quite similar consequences, but now it could be worse because (Russian President Vladimir) Putin belongs to a generation that had no war under its belt.”

Trump’s decision could prove controversial with European allies and others who see value in the treaty, said Steven Pifer, a former U.S. ambassador to Ukraine and now a senior fellow at the Brookings Institution who focuses on nuclear arms control.

“Once the United States withdraws from the treaty, there is no reason for Russia to even pretend it is observing the limits,” he wrote in a post on the organization’s website. “Moscow will be free to deploy the 9M729 cruise missile, and an intermediate-range ballistic missile if it wants, without any restraint.”

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U.S. officials have previously alleged that Russia violated the treaty by deliberately deploying a land-based cruise missile in order to pose a threat to NATO. Russia has claimed that U.S. missile defences violate the pact.

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In the past, the Obama administration worked to convince Moscow to respect the INF treaty but made little progress.

“If they get smart and if others get smart and they say let’s not develop these horrible nuclear weapons, I would be extremely happy with that, but as long as somebody’s violating the agreement, we’re not going to be the only ones to adhere to it,” Trump said.