Russia called a U.N. Security Council meeting on the matter following the U.S. test of a missile banned by the 1987 intermediate-range Nuclear Forces Treaty, which both countries withdrew from on Aug. 2.
Russia's deputy U.N. ambassador, Dmitry Polyansky, criticized what he called American "hypocrisy," saying the U.S. "consistently and deliberately violated the INF treaty for some time." He said the missile test on Aug. 18, so soon after the treaty's expiration, proved it.
The council meeting put on vivid display the deep distrust between the two nuclear powers, and the anxiety of other nations about an escalating arms race including with China.
America's NATO allies joined Cohen in blaming Russia for what France's deputy ambassador, Anne Gueguen, called "the death of the treaty."
Britain's political coordinator Stephen Hickey, said Russia's actions "are in line with a pattern of aggression that represents a clear threat to international peace and security" and undermine its claim "that it is a responsible international partner."
Gueguen warned that "it would be a dangerous step backward to engage in a new arms race."
Russia's envoy directed key remarks to NATO's European council members — Britain, France, Germany, Belgium and Poland. Polyansky asked whether they understand that by supporting the U.S. "step by step, you are returning to a historic situation when missiles were targeting European cities from different sites."
"From our part, we would not be the first to make use of such measures," he added. "However, considering that our American colleagues are clearly rubbing their hands and want to flex their muscles, then it's possible that that situation ... could happen quite soon."
Polyansky urged the Europeans to realize "that because of the U.S.'s geopolitical ambitions we are all one step from an arms race that cannot be controlled or regulated in any way."
Cohen told the council that perhaps a better use of its time would be to ask Russia "to address the threats it poses to international peace and security," including where its ground-launched cruise missiles are, and how many it's deployed.
He said Russia is also pursuing "novel strategic nuclear weapons."
"These include a nuclear-armed and powered underwater drone designed to destroy adversary coastal cities and ports in a radioactive tidal wave; a nuclear-armed and -powered, ground-launched, intercontinental-range cruise missile; and a nuclear-armed, air-launched ballistic missile," he said.
Cohen also asked Russia to tell the council what caused the Aug. 8 explosion at a Russian navy test site on the White Sea in the country's northwest. "What system was it, and what purpose does that system serve?"
Polyansky did not mention the incident.
Russian President Vladimir Putin insisted Wednesday that the explosion, which killed two servicemen and five nuclear engineers and injured six, hasn't posed any radiation threat, but he remained coy about the circumstances of the incident.
Changing and contradictory accounts of the explosion by Russian officials drew comparisons to Soviet attempts to cover up the 1986 explosion and fire at the Chernobyl nuclear power plant in Ukraine, the world's worst nuclear disaster.
Looking ahead, Polyansky said the demise of the INF treaty put "at risk" the START treaty on long-range nuclear weapons that is scheduled to expire in 2021. President Donald Trump said recently he has been discussing a new agreement to reduce nuclear weapons with China and Russia.
Cohen told the council that China is rapidly expanding and diversifying its nuclear stockpile, including with new delivery systems, and it is examining how hypersonic systems, air-launched ballistic missiles and low-yield nuclear weapons fit it.
"These developments by the Russian Federation and China — coupled with their aggressive and coercive behaviors — are key drivers behind a deteriorating security environment," he said.
Contrary to Russia's "outrageous assertions," Cohen said, the United States has made clear its interest in effective and verifiable arms control that includes Russia and China and goes beyond treaties focused on limited types of nuclear weapons or missile ranges.
China's ambassador, Zhang Jun, said his country's military policy is defensive, its nuclear strategy is "completely transparent," and its nuclear arsenal "is extremely limited in scale and never poses a threat."
He said it was "unacceptable" for the U.S. to use China's weapons program as "an excuse" to leave the IMF treaty.
China opposes an arms race, Zhang said. But, he added, "at this stage China has no interest, and will not participate, in the so-called trilateral arms control negotiations" with the U.S. and Russia.