Russia’s deputy foreign minister said on Monday that the United States should “cool down” after Washington warned Moscow against nuclear weapons in Ukraine, the state agency RIA Novosti reported.

“We tell our American partners again and again, to use the most neutral word, that they should, as they say, cool down,” Sergei Ryabkov said, referring to the war in Ukraine.

Washington shouldn’t escalate the conflict and “bring it closer to a dangerous line,” Ryabkov told state broadcaster Channel One.

President Vladimir Putin made a thinly veiled threat to use nuclear arms in a speech Wednesday in which he announced the mobilization of reservists following Ukrainian gains on the ground.

Secretary of State Antony Blinken, in an interview broadcast Sunday, confirmed reports that the United States had sent private warnings to Russia to steer clear of nuclear war.

“We have been very clear with the Russians publicly, and, as well as privately, to stop the loose talk about nuclear weapons,” Blinken told the CBS News program “60 Minutes” in New York on the sidelines of the UN General Assembly.

“It’s very important that Moscow hears from us and knows from us that the consequences would be horrific. And we’ve made that very clear,” Blinken said.

“Any use of nuclear weapons would have catastrophic effects for, of course, the country using them, but for many others as well.”

Jake Sullivan, President Joe Biden’s national security adviser, said in a separate interview Sunday that the United States has warned Russia at “very high levels” of “catastrophic consequences” for using nuclear arms.

AFP contributed reporting.