NATO, led by the United States, said Friday that it is concerned a Russian missile system could violate a landmark arms-control treaty credited with helping end the Cold War.

“Allies have identified a Russian missile system that raises serious concerns,” said a statement from the North Atlantic Council, the alliance’s political decision-making body. “NATO urges Russia to address these concerns in a substantial and transparent way, and actively engage in a technical dialogue with the United States.”

At issue is the 1987 Intermediate-range Nuclear Forces (INF) Treaty, which bans ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers.

The United States has repeatedly accused Russia of violating the pact, including with the deployment of a nuclear-tipped cruise missile. U.S. officials have said the violation puts European allies at risk of a nuclear strike from Russia with little to no warning.

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Last week, in marking the 30th anniversary of the treaty’s signing, the State Department confirmed the United States is responding to the alleged violations by beginning research on a missile that would violate the treaty. The research itself is not a violation.

Russia insists that it has not violated the INF Treaty and that the United States is out of compliance by deploying missile defenses to Europe.

In Friday’s statement, NATO said a situation where the United States and others comply with the treaty while Russia violates it “would be a grave and urgent concern.”

“The alliance is united in its appreciation that effective arms control agreements remain an essential element to strategic stability and our collective security,” the statement said. “In this spirit, our actions, including national measures taken by some allies, seek to preserve the INF Treaty, strengthen the alliance and incentivize Russia to engage in good faith.”

In a separate statement, U.S. Ambassador to NATO Kay Bailey Hutchison said the North Atlantic Council statement shows the United States and its allies are “speaking to Russia with one voice about its dangerous and destabilizing behavior.”

“Our allies reaffirmed that the U.S. is in compliance with our obligations under the INF Treaty and that Russia’s behavior raises serious concerns,” she said.

She also said the Trump administration is committed to upholding its obligations under the INF Treaty, promising the United States “will not cross any thresholds” that would violate the accord.

“We are doing our part to address any questions regarding our compliance with the INF Treaty in a transparent, substantive and constructive manner,” she said. “It is up to Russia to do the same.”