NATO said Friday that it is concerned about a Russian missile system that could carry nuclear warheads, and which it says could violate a landmark Cold War arms treaty.
The U.S.-led military alliance said in a statement that "allies have identified a Russian missile system that raises serious concerns."
It urged Russia "to address these concerns in a substantial and transparent way, and actively engage in a technical dialogue with the United States."
NATO fears the system contravenes the 1987 Intermediate-range Nuclear Forces (INF) Treaty. The Cold War-era pact bans an entire class of weapons — all land-based missiles with a range between 500 and 5,500 kilometers (310-3,410 miles).
The statement said a situation whereby the U.S. and other parties abided by the treaty but Russia did not "would be a grave and urgent concern."
The concern centers on Russia's 9M729 missiles. Washington has given evidence that Russia is developing the ground-fired cruise missile and said the system could give Moscow the ability to launch a nuclear strike in Europe with little or no notice.
U.S. envoy to NATO, Kay Bailey Hutchison, described Russia's behavior as "dangerous and destabilizing."
"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 in a statement.
Russia has rejected the accusations, which had been levelled earlier by the U.S.
Russian President Vladimir Putin insisted Thursday that Russia has observed the INF Treaty, charging that U.S. claims of Russian violations are part of a "propaganda" campaign to pave the way for a U.S. withdrawal from the treaty.
Putin also reaffirmed Russia's claim that the U.S. itself had violated the pact, allegations that Washington has denied.
The head of the Russian Foreign Ministry's arms control department, Mikhail Ulyanov, detailed Russia's allegations Friday, claiming that U.S. missile defense facilities in Romania containing interceptor missiles could be modified to house ground-to-ground intermediate-range cruise missiles.
In remarks carried by the Interfax news agency, Ulyanov also claimed that U.S. launches of target vehicles as part of tests could also be seen as a violation.
The U.S. has rejected all the Russian claims.
The NATO statement comes after a meeting between the U.S. and Russia in the Special Verification Commission this week, and is part of broader efforts to bring Moscow into compliance with the treaty.
Tensions between NATO and Russia have remained high since Russia annexed Ukraine's Crimean Peninsula in 2014 and supported pro-Russia insurgents in eastern Ukraine.
NATO has responded by deploying thousands of troops to Estonia, Latvia, Lithuania and Poland as a deterrent.
Vladimir Isachenkov in Moscow contributed to this report.