With President Joe Biden, NATO, and the European Union gathering late this week to talk about its response to Vladimir Putin's invasion of Ukraine, Russia is warning it could use a tactical nuclear weapon if NATO interferes.
"If Russia is provoked by NATO, if Russia is attacked by NATO, we are a nuclear power, why not?" Russian Ambassador Dmitry Polyanskiy told Sky News on Friday.
"I don't think it's the right thing to be saying, but it's not the right thing to threaten Russia, and to try to interfere. When you're dealing with a nuclear power, of course, you have to calculate all the possible outcomes of your behavior. That's what I am going to say."
Former NATO Supreme Allied Cmdr. Wesley Clark predicted that saber rattling Thursday, saying the world knows Russia's nuclear deterrence position.
"We have to anticipate what he might do," Clark told CNN late this week. "We have to anticipate what he might do. The use of chemical weapons seems to be a little bit premature, except perhaps in going after Mariupol, but it's not that significant. I think the chemical weapons threat is a more far-fetched play.
"If he really wanted to deter NATO involvement, and he believes that he can shatter NATO, then he would perhaps use a low-yield nuclear weapon."
The use of a nuclear weapons would be directed at NATO allies, perhaps in weapons-staging areas in Poland, the closest neighboring NATO ally. Biden is delivering a speech Saturday in Poland amid the saber rattling.
"Where would he use it? Probably not in Ukraine, but perhaps on the staging areas or some populated area in Poland," Clark added. "This is what's usually done in the Russia exercises."
Talk of tactical nuclear weapons use is not new, as much as it potentially pending.
"Putin is using nuclear deterrence to have his way in Ukraine," Brown University senior lecturer Nina Tannenwald told The New York Times last week. "His nuclear weapons keep the West from intervening."
University of Hamburg nuclear expert Ulrich Kühn warned of the increasing "possibility."
"The chances are low but rising," Kühn told the Times. "The war is not going well for the Russians, and the pressure from the West is increasing."
"It feels horrible to talk about these things, but we have to consider that this is becoming a possibility."
Regardless, Putin's aggressions cannot go unchecked, according to former Obama-era Director of National Intelligence James Clapper.
"When do you stop?" Clapper said this week. "You can't just keep turning the other cheek. At some point we'd have to do something."
Clark added NATO's fear of nuclear war is an effective deterrent for Putin.
"The way they postulate in their exercises is that if Russia starts to lose because of NATO support, the opposition, then 'pow!' They send a nuclear weapon in," Clark told CNN on Thursday. "Then NATO says, Oh my goodness, we don't want a nuclear war — that'll be the Third World War. OK, since you're that serious about it, we'll back off.
"So this is the way the Russians have educated themselves to think about what they would do in a circumstance like this. And this is why there's so much concern on the part of the administration and other NATO leaders, because they all know this."