The United States has warned Russia there will be "catastrophic" consequences if it uses nuclear weapons after setbacks in its war in Ukraine.
Russian President Vladimir Putin issued renewed threats that he could resort to weapons of mass destruction as he escalated the conflict last week by calling up military reservists and moving to annex occupied areas that are staging votes to join Russia.
With his mobilization effort facing domestic backlash and Kyiv's forces pressing to make new gains after their stunning counteroffensive, two top U.S. officials said Sunday that Washington has made it clear to Moscow just how stark a response it would face in the event of a nuclear attack.
National security adviser Jake Sullivan told NBC News' "Meet the Press" on Sunday that the consequences "would be catastrophic if Russia went down the dark road of nuclear weapons use."
Pressed by host Chuck Todd about what those countermeasures would be, Sullivan would only say, "In private channels we have spelled out in greater detail exactly what that would mean."
Secretary of State Antony Blinken used similar language in an interview with CBS News' "60 Minutes."
"It's very important that Moscow hear from us and know from us that the consequences would be horrific, and we've made that very clear," he said, adding that the U.S. response would be "catastrophic" without elaborating.
Putin has made a string of nuclear threats against Ukraine and the West as a whole since he launched his invasion more than seven months ago. But last week, he dramatically intensified Russia's efforts, signaling he was willing to escalate rather than accept battlefield defeat.
In an address to his nation last Wednesday, Putin said that if Russia's "territorial integrity" was threatened, "we will certainly use all the means at our disposal" to retaliate — and added that “it’s not a bluff."
Ukrainian President Volodymyr Zelenskyy has said he believes the Russian president.
"I don’t think he’s bluffing," Zelenskyy told CBS' "Face the Nation" on Sunday. "He wants to scare the whole world. These are the first steps of his nuclear blackmail."
Russia has the largest nuclear arsenal in the world with almost 6,000 nuclear warheads and 1,500 of them currently deployed, according to the Stockholm International Peace Research Institute, an independent think tank that tracks global stockpiles.
The Kremlin's thinly veiled threats come against the backdrop of votes being held in four regions in Ukraine's south and east that its forces at least partly control: Luhansk and Donetsk, Zaporizhzhia and Kherson. Western officials have dismissed these as sham votes with predetermined outcomes.
Putin's warnings also come after a litany of setbacks for Russia.
The looming annexation and the nuclear threats have been viewed by analysts as a combined effort to deter Western support for Ukraine, and to stem the tide of a pair of counteroffensives that have left Russia's long-term grip on those occupied territories in growing doubt.
Asked if Moscow would consider using nuclear weapons to defend these regions, Russian Foreign Minister Sergei Lavrov said Saturday that they would be under the “full protection of the state.”
Two months into the invasion, Putin's army withdrew from a costly and ultimately failed assault toward the Ukrainian capital, Kyiv, instead choosing to focus its forces in the east of the country where it has supported pro-Russian separatists since 2014.
However in recent weeks, Ukraine has mounted a strong fightback in those areas too, causing heavy Russian losses and rare domestic disquiet from pro-war nationalists.
That has seen unknown thousands of Russian civilians rounded up to be sent to the front lines. It has also triggered an exodus of Russians attempting to flee the draft, clogging border crossings and snapping up available flights.