Russia and China on Thursday asked the UN Security Council to meet over U.S. officials’ statements indicating plans to develop and deploy medium-range missiles. The Pentagon said Monday it had tested a cruise missile with a range of more than 500 kilometers, the first such test since the U.S. pulled out of the 1987 Intermediate-Range Nuclear Forces Treaty (INF).

Russia has accused the United States of provoking an “uncontrolled” arms race during a United Nations Security Council meeting, the latest in an exchange of barbs between Moscow and Washington over the demise of a Cold War-era arms control treaty.

“Are you aware that because of the geopolitical ambitions of the U.S. we are all just one step away from an uncontrolled and unregulated arms race?” Russia’s UN representative at the Security Council said at the meeting Thursday.

The future of the last remaining U.S.-Russian nuclear arms control treaty — the New START — is “also at risk” of expiring without extension in 2021, said the diplomat, Dmitry Polyansky.

“In any case, according to President [Donald] Trump, America is ready for an arms race,” Polyansky told the 15-member UN council.

Washington’s envoy to the international body, Ambassador Jonathan Cohen, accused Russia of deciding to violate the INF Treaty more than a decade ago by fielding medium-range missiles in Europe.

Cohen also called on Moscow to address the mysterious Aug. 8 rocket engine explosion in northern Russia that killed at least five nuclear engineers. Russian officials have given a muted response in the weeks since the accident and U.S.-based nuclear experts suspect Russia was testing a nuclear-powered cruise missile.

“What system was it, and what purpose does that system serve?” the U.S. ambassador asked.

Reuters contributed reporting to this article.