CNN  — 

The die is being cast in Ukraine for a long, bloody war of attrition that threatens mass civilian deaths, a catastrophic refugee crisis and a geostrategic shake-up that would cement a new age of confrontation between the US and Russia.

A week into a war unleashed by President Vladimir Putin’s 30-year brooding over the collapse of the Soviet Union, a shock-and-awe blitzkrieg by Russian troops has been averted by the courage of the Ukrainian people. Failures of equipment and morale have also slowed Putin’s forces, causing what appears to be a tactical retrenchment on the Russian side that is bringing civilians into the firing line.

At least one huge explosion split the air in Kyiv in the early hours of Thursday morning, after a day that revealed new damage from Russian rocket and missile attacks that hit apartment blocks, shops, a cathedral and a heating pipeline. As thousands of Kyiv residents sleep in subway shelters and learn the terrible routines of war – the randomness of sudden civilian deaths and the psychologically corrosive wail of air raid sirens and overnight shelling – the likely next dreadful stage of the war is coming into view.

The history of Russia’s military doctrine, Putin’s own ruthless disregard for human life and growing signs that Moscow is targeting civilians point to a bitter winter campaign to strangle Ukraine of its resolve and independence.

It’s often noted that Russia’s invasion is the most significant land war in Europe since World War II. Now there is growing dread, in Washington especially, that scenes of destruction and carnage last witnessed nearly 80 years ago could soon unfold again on a blood-soaked continent that has recently enjoyed an unusual period of peace.

Official US sources speaking on condition of anonymity and lawmakers and officials familiar with the latest intelligence concurred on Wednesday about the horror the future may hold for Ukrainian civilians. Washington’s envoy to the United Nations, Linda Thomas-Greenfield, for instance, accused Russia of bringing horrific weapons banned under the Geneva Conventions into Ukraine, including cluster munitions and vacuum bombs.

Democratic Rep. Adam Smith of Washington state, who chairs the House Armed Services Committee, told CNN’s Jake Tapper on “The Lead” that Putin was regrouping in a manner that was especially fateful for Kyiv.

“The anticipation is that they will surround the city and, if you look at what Russia has done in other places, like Chechnya and Syria – indiscriminate bombing, attacking civilian targets – they get more brutal to accomplish their objectives.”

Florida Sen. Marco Rubio, the top Republican on the Senate Intelligence Committee, warned that since Putin was backed into a corner by the underperformance of the Russian army and faced military humiliation and an economic collapse under Western sanctions, he could become more extreme.

“It’s my personal opinion that this guy is going to have to create some new crisis, do something to reset the strategic balance and force everyone to the table with him,” Rubio told Tapper. “It could be a combination of things, including a siege of Kyiv where 3 million people are being starved to death.”

‘They will just pummel the city’

Colorado Democratic Rep. Jason Crow, a veteran of the Iraq and Afghanistan wars, predicted that Putin’s natural move would be to resort to more combat power.

“This is going to get worse and worse for the Ukrainians,” Crow told CNN’s Wolf Blitzer on “The Situation Room.”

And retired Col. Cedric Leighton, a CNN military analyst, pointed out that Moscow, whose forces seized the southern city of Kherson on Wednesday, was seeking to slowly move in on Kyiv from the north, the east and the south. “This is a boa constrictor that is biting off one piece at a time and is basically trying to choke the entire country,” Leighton said.

US and other Western officials told CNN on Wednesday that the Russian strategy was shifting to one of “slow annihilation” of Ukraine. Rising attacks on civilians, subsequent food crises and other inflicted misery could mean that the courage and resistance shown by Ukrainians will make their plight even more brutal.

Ukraine’s will to fight “is extending this,” a senior Western intelligence official said. “But the cruel military math of this will eventually come to bear, absent some intervention, absent some fundamental change in the dynamic.”

Russia’s increasing frustration could create a horrific scene in Kyiv that would likely see war crimes being committed, retired Gen. David Petraeus, a former CIA director who also served in Iraq and Afghanistan, told CNN’s Anderson Cooper.

“They will just pummel the city; they will destroy (it) section by section. They will starve the people out, depopulate it,” Petraeus said.

Low hopes for diplomacy

The chance that a diplomatic intervention could avert what is to come seems unlikely. Though Ukrainian and Russian officials are expected to hold a second round of talks in Belarus on Thursday, expectations are very low. US Secretary of State Antony Blinken said the attitude of the Russians in the first set of talks left little hope of a breakthrough but that the US would participate in any track that the Ukrainians believed was in their interests.

“The demands that Russia put on the table were beyond excessive,” Blinken said on Wednesday. “They were, of course, nonstarters, and what we’ve seen repeatedly is that Russia goes through the pretense of diplomacy to distract and continue on its aggressive path.”

The hammer blow of US and other Western sanctions that slammed into the Russian economy this week, and Putin’s consequent nuclear saber rattling, are likely to also shut off relations with the Russian government for months, if not permanently.

The likelihood of a prolonged war of attrition in Ukraine will require strategic readjustments in Western capitals as well as in Kyiv and Moscow.

The US-led diplomatic front against Russia has been staggeringly successful so far in uniting NATO allies and Republicans and Democrats in the Congress in a rare common position against Russia. But while Ukrainian civilians will bear the brunt of ruthless Russian tactics, indirect costs will begin to rise for Americans and others as the conflict grinds on. Republicans who stood to applaud at Biden’s State of the Union address on Tuesday as he vowed to stand up to Putin will also be quick to lambast the President over high gasoline prices – exacerbated by the Ukraine crisis – as midterm elections approach in November.

One of Putin’s goals in prolonging the situation will be to try to open gaps among NATO members over a period of months. There is no sign of that happening so far, but Biden will have to constantly manage the Western coalition against Russia. A long-term siege of Kyiv and other cities could also worsen a refugee crisis that has already seen 1 million people flee Ukraine, according to the UN. Massive refugee flows could severely strain nations in Eastern Europe that won their freedom from domination by the Kremlin when the Soviet Union collapsed three decades ago.

The possibility that the West will have to sit back and watch a humanitarian disaster unfold in Kyiv and other Ukrainian cities will also shape the politics of the crisis. Such scenes might boost calls for a more strident Western intervention. But the strategic reality, which is being exploited by Putin, is that putting troops in Ukraine or trying to establish a no-fly zone would involve clashes between US and Russian forces – and potentially set off a deadly escalation with Russia, which has the world’s largest stockpile of nuclear warheads.

Already, a Cold War-style proxy war is heating up.

The US has delivered hundreds of Stinger anti-aircraft missiles to Ukraine for the first time, including more than 200 on Monday, a US official and a congressional source told CNN on Wednesday. The US gave the green light to Baltic countries to send American-made weaponry to Ukraine, including Stingers, earlier this year. But until now, the Biden administration had held off on sending Stingers to Ukraine, although it has provided other lethal weaponry.

The latest developments in Ukraine mean that for the first time since the Soviet war in Afghanistan in the 1980s, the United States is involved in an indirect yet active effort to kill Moscow’s troops by arming one of the Kremlin’s enemies.

Given the lack of any realistic diplomatic off-ramp, the sight of some of the most extreme modern weapons around Ukraine is adding to the sense of dread. A Russian thermobaric multiple rocket launcher was spotted by a CNN team south of Belgorod, Russia, near the Ukrainian border early Saturday afternoon. Such weapons are known as “vacuum bombs” because they suck in oxygen from the surrounding air to generate a powerful explosion and large pressure wave that can be devastating to humans. There is no evidence that thermobaric weapons have been used so far in the conflict in Ukraine, but just the possibility that they could be underscores the grave threat it faces.

Paul Kolbe, former chief of the CIA’s Central Eurasia division, told CNN’s Erin Burnett that militaries don’t bring kit into conflicts that they don’t intend to use.

“The prospect of using these types of weapon – whether cluster munitions or a thermobaric weapon – in a civilized city, in a civilian area, is horrific to think about. It should shock the conscience of the entire world.”

Katie Bo Lillis, Jim Sciutto, Jeremy Herb, Barbara Starr and Kylie Atwood contributed to this report.