NATO Secretary-General Jens Stoltenberg on Wednesday urged Russia to make quick changes to comply in full with the 1987 Intermediate-Range Nuclear Forces (INF) treaty.
Stoltenberg called on Russia to provide details about a new missile system the United States and other allies claim violates the accord.
The NATO chief voiced his dissatisfaction that Moscow had not responded to the Alliance's concerns over its SSC-8 missile program (known in Russia as the 9M729).
"NATO has urged Russia repeatedly to address these concerns in a substantial and transparent way, and to actively engage in a constructive dialogue with the United States," Stoltenberg said at talks between Russian and NATO envoys in Brussels.
"We regret that Russia has not heeded our calls" for transparency about the missile system, he said.
Stoltenberg added that Russia's reluctance to discuss the missile system reinforces NATO's belief that it "poses a serious risk to the strategic stability of the Euro-Atlantic area."
Russia denies that the missile system violates the INF treaty, which prohibits the US 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).
Read more: What is the INF nuclear treaty?
President Donald Trump vowed last month to withdraw from INF, accusing Russia of "violating the terms of the treaty." The Kremlin responded, saying Russia would be forced to respond in kind if the US began developing new missiles.
The NATO and Russian envoys also discussed their respective large-scale military exercises.
The two sides had an "open exchange" of views on Ukraine, Russia's Vostok military exercises and NATO's ongoing Trident Juncture drills, as well as on Afghanistan and hybrid security threats, a NATO statement said.
The talks took place against the backdrop of renewed tensions between the West and Russia mainly over Moscow's annexation of Crimea in 2014 and its involvement in eastern Ukraine.
In October, NATO launched its largest exercises since the Cold War in Norway.
Russia's 2018 edition of Vostok mobilized 300,000 troops and included joint exercises with the Chinese army — the biggest such drills since the Soviet Union broke up in 1991.
ap/bw (AP, AFP, Reuters)