Senior Western officials are increasingly alarmed that Russia's losses in Ukraine are making President Vladimir Putin more dangerous, some going as far as to compare him to a caged animal ready to lash out.
The warnings, from Washington and Brussels, come as new intelligence estimates suggest that up to 20% of Russian troops sent into Ukraine have been killed, wounded or captured as Ukraine fights Moscow to a near standstill.
"I don't know if you can go as far [as to say] stalemate, but it's clear that after one month, Russia has achieved almost none of their strategic objectives," said a senior NATO official, who spoke to reporters Wednesday on the condition of anonymity in order to discuss intelligence.
"They are stalled in Kyiv. They are stalled in Kharkiv. They are stalled in Chernihiv," the official said.
And in a break with some U.S. defense officials, who have declined to talk about Russian casualties in Ukraine because of “low confidence” in the estimates, NATO officials say the price on the battlefield has been high.
NATO on Wednesday estimated that between 7,000 and 15,000 Russian troops have been killed in battle, basing the assessment on intelligence from Ukraine and its own observations, including information accidentally released by Moscow.
When wounded, captured and missing soldiers are factored in, the number of Russian troops taken off the battlefield is between 30,000 and 40,000, the alliance believes.
But Western officials warn that rather than pull back, Putin has decided to respond to failure with even greater brutality and tactics reminiscent of a previous era.
"They are achieving more results in the south, but the price of it is absolutely horrendous," the senior NATO official said, accusing Moscow of trying to carpet-bomb the Ukrainian city of Mariupol into submission.
"What they do is World War II, 70-year-old techniques," the official said. "To reach this extreme, you need to be cornered and you need to be pushed to break all moral human rules to go to such brutality."
The official further warned that Russia's failure to quickly subjugate Ukraine is feeding into Putin's already deep hatred of Western values, increasing the chances he may choose to expand the conflict beyond Ukraine.
"The alliance is absolutely at risk," the official said.
There is growing concern that Putin may turn to weapons of mass destruction, whether they be nuclear, chemical or biological.
"Russia must stop its nuclear saber rattling. This is dangerous and it is irresponsible," NATO Secretary-General Jens Stoltenberg told reporters in Brussels Wednesday, ahead of an extraordinary meeting of alliance heads of state.
"Any use of nuclear weapons will fundamentally change the nature of the conflict," Stoltenberg said. "NATO is there to protect and defend all allies, and we convey a very clear message to Russia that nuclear war cannot be won and should never be fought."
Putin put Russia's nuclear deterrence forces on high alert just three days after Russian tanks first rolled into Ukraine, and some Russian officials have floated the idea of using tactical nuclear weapons if necessary.
"If it is an existential threat for our country, then it can be used in accordance with our concept," Kremlin spokesman Dmitry Peskov told the U.S.-based cable news channel CNN on Tuesday.
U.S. defense officials said earlier this week that so far, they had seen no movement by Russia that would cause them to change Washington's own nuclear deterrence posture.
But the U.S. has expressed growing concern about the possibility Russia will use chemical weapons.
"I think it's a real threat," U.S. President Joe Biden told reporters Wednesday in Washington before leaving the White House to attend the NATO summit in Brussels.
While not downplaying the danger, a senior U.S. defense official cautioned Wednesday that, at this point, a Russian attack using chemical or biological weapons does not appear to be looming.
“We haven't seen any imminent signs that there's going to be a chem-bio [chemical or biological] event caused by the Russians,” the official told reporters, speaking on the condition of anonymity to discuss sensitive information.
NATO officials, however, said the alliance has reason to believe an eventual attack is not out of the question and that they are preparing for two equally frightening scenarios.
"One is what is openly called a false flag operation — this would be an accident on a chemical plant," the senior NATO official said, pointing to the large amounts of ammonia, nitrates and other agricultural chemicals in Ukraine.
"If you have a massive release of those agents, it is very dangerous for the population," the official added, warning that chemical clouds could then put other countries in the region at risk.
But NATO is also worried Russia could throw caution to the wind and use missiles or shells to target Ukraine with highly lethal neurotoxins.
"When you use them, they are so characteristic that the attribution is immediate," the official said, adding that the biggest question for Western defense officials is whether Russia is going to want to stay below the threshold of attribution for the weapons it unleashes.