U.S. President Donald Trump’s national security adviser met in Moscow with top Russian officials Monday, less than 48 hours after Trump declared he intended to pull the United States out of a 1987 nuclear weapons treaty.

National Security Adviser John Bolton and his Russian counterpart, Security Council chairman Nikolai Patrushev, discussed arms control agreements, Syria, Iran, North Korea and the fight against terrorism, according to the Security Council.

During the talks, Patrushev emphasized the importance of maintaining the Intermediate-Range Nuclear Forces (INF) Treaty, the Security Council said in a statement carried by Russian news agencies.

In his announcement about withdrawing from the agreement, Trump alleged that Russia violated its terms. The treaty prohibits the U.S. and Russia from possessing, producing or test-flying ground-launched nuclear cruise missiles with a range of 500 to 5,500 kilometers (300 to 3,400 miles.)

Patrushev reaffirmed Russia’s “readiness for joint work to consider mutual complaints regarding the treaty’s implementation,” the Security Council said.

“It was underlined that its abrogation would deal a serious blow to the entire international system of nuclear non-proliferation and arms control,” the council’s statement said.

Patrushev and Bolton also discussed a possible five-year extension of another pivotal arms control agreement between Russia and the U.S. — the New START Treaty that went into force in 2011 and is set to expire in 2021, the statement said.

Bolton also held talks later in the day with Russian Foreign Minister Sergey Lavrov and is set to meet with President Vladimir Putin on Tuesday.

Putin’s spokesman, Dmitry Peskov, warned Monday that the U.S. withdrawal from the treaty would “make the world a more dangerous place.”

He added that Russia would have to take countermeasures to “restore balance” if the U.S. opts out of the agreement.

Peskov reaffirmed Moscow’s strong denial of any treaty violations.

“We categorically disagree with the claim that Russia has violated the INF Treaty,” he said. “Russia has fully adhered to the treaty’s provisions.”

He noted that Russia long has voiced concern about what it sees as U.S. violations of the treaty. Russia has charged that U.S. missile defense facilities in Romania could be modified to house ground-to-ground intermediate-range cruise missiles.

NATO spokeswoman Oana Lungescu said Monday that the military alliance has repeatedly expressed concern about Russia’s nuclear-capable 9M729 missile.

“In the absence of any credible answer from Russia on this new missile, allies believe that the most plausible assessment would be that Russia is in violation of the INF Treaty,” she said.

Lungescu didn’t comment on Trump’s threat to withdraw from the treaty, saying only that the “allies continue consultations.”

The European Union warned Trump to assess the potential impact of abandoning a 40-year-old arms control agreement.

The EU said that along with urging Russia to stick to the treaty, it encouraged “the United States to consider the consequences of its possible withdrawal from the INF on its own security, on the security of its allies and of the whole world.”

The bloc described the treaty as an essential cornerstone of Europe’s security structure, adding, “the world doesn’t need a new arms race that would benefit no one and on the contrary, would bring even more instability.”

U.N. Secretary-General Antonio Guterres “still hopes that the two countries will engage to solve the disagreements,” U.N. deputy spokesman Farhan Haq said Monday.

Haq noted that Guterres has urged the U.S. and Russia to resolve their dispute over the INF, to extend the New START treaty and to take new steps to reduce nuclear stockpiles.

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