WASHINGTON — The staggeringly high rate of Russian casualties in Ukraine means that President Vladimir V. Putin may not be able to achieve one of his key war objectives: seizing the entire eastern region of the country this year, officials in the Biden administration and military experts say.
With 500 Russian troops killed or wounded every day, according to the latest estimate by American intelligence and military officials, Russia’s war effort has decelerated to a grinding slog, the officials said.
Russia’s glacial pace in the east has been further stymied by the arrival of American multiple-launch rocket systems, which have allowed Ukrainian troops to take back some territory and made it more difficult for Russian soldiers to reach other areas.
Earlier this summer, Russian forces captured the Luhansk region of Ukraine, the easternmost part of the country. But in neighboring Donetsk, their progress has stalled, in no small part because of heavy casualties, American military officials said.
“I think it’s safe to suggest that the Russians have probably taken 70 or 80,000 casualties in less than six months,” Colin Kahl, the under secretary of defense for policy, told reporters at the Pentagon on Monday, referring to deaths and injuries.
“They have made some incremental gains in the east, although not very much in the last couple of weeks, but that has come at extraordinary cost to the Russian military because of how well the Ukrainian military has performed and all the assistance the Ukrainian military has gotten.”
Two American officials said that estimate of Russia’s losses included about 20,000 deaths. Of that number, 5,000 are believed to be mercenaries from the Wagner Group, a private force with ties to Mr. Putin, and foreign fighters, one of the officials said, speaking on the condition of anonymity because she was not authorized to discuss sensitive military assessments.
American officials say their casualty estimates are based on satellite imagery, communication intercepts, social media and on-the-ground media reports.
The Russian government classifies troop deaths as state secrets, and the country’s war dead are rarely mentioned on state television. Russia last announced an official figure in March, when it said that 1,351 Russian soldiers had been killed in the war. At the time, American officials estimated that the number was closer to 5,000.
Ukraine has also sustained heavy casualties, the officials say. The Ukrainian government has been reluctant to disclose figures but has said 100 to 200 of its troops were being killed a day.
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Because Ukraine has been at war with Russian separatists for almost a decade, it has a large pool of seasoned veterans available to the fight. Still, American officials say the conflict has become the bloodiest land war in Europe since World War II.
But for Russia, the high casualty number has meant slower progress. The result, Mr. Kahl said, is that “conditions in the east have essentially stabilized” and Russia has been forced to redeploy its forces to the south, as Ukraine intensifies a campaign to retake territory there.
Mr. Putin has also augmented his ranks with former soldiers. But the battlefield effectiveness of the arrivals “is quite poor,” a senior defense official told reporters last month.
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“The Russian Army is seriously depleted,” said Seth G. Jones, the director of the international security program at the Center for Strategic and International Studies. “That has implications on their ability to fight an effective ground campaign in Ukraine.”
As the Russian military suffers steep casualties, American and European officials said, it has struggled to bring reservists and new recruits into the fight.
Russia has already committed nearly 85 percent of its fielded army to the war, drawing on troops from the country’s far east and deployments around the world, defense officials say. Before invading Ukraine in February, the Russian military had about 900,000 active-duty troops.
“The Russians probably don’t have enough effective combat forces to fully take Donetsk,” Mr. Jones said in an interview.
Moscow has also recruited Chechen troops and fighters from Syria, whose president is allied with Mr. Putin. By relying on these fighters, officials said, Mr. Putin has avoided a domestic outcry over casualties and the need, so far, to call a general mobilization, which is akin to a draft.
“They increased the age for recruitments in Russia and have been doing other things to sweeten the pot” for volunteers, said Evelyn Farkas, the director of the McCain Institute and a senior Pentagon official for Ukraine in the Obama administration. “They’re pulling people from all over.”
But, Ms. Farkas added: “Unless they have a mass mobilization, which I don’t see them being able to do at this point politically, they’re going to be at a loss.”
After seizing Luhansk, Russia said it was pausing the campaign in the east to regroup and rearm. But it continued to shell cities and towns in the region, and its troops continued to fight. Meanwhile, Ukrainian troops went on the offensive in towns in Donetsk, taking back slivers of land there.
As fighting intensified in southern Ukraine, a series of explosions on Tuesday rocked a Russian air base in Crimea, a peninsula in the south that Russia illegally annexed in 2014. Satellite images show at least eight wrecked warplanes at the site of the explosion.
Ukraine has not officially asserted responsibility for the explosions, but a senior Ukrainian military official said the country’s special forces and local partisan resistance fighters loyal to the government were behind the attack.
With Ukraine on the offensive to regain territory in the south, officials say Mr. Putin may have to shift more troops there.
The Russian military has lost so many troops that in some cases units have tried to force captured Ukrainians to fight, according to retired Gen. Philip M. Breedlove, who was NATO’s supreme allied commander for Europe when Russia annexed Crimea.
“They have a tremendous problem of manpower and an even tougher problem that the manpower they have is not well trained,” General Breedlove said in an interview. “Their best units have already been bloodied.”
Pentagon officials say that it becomes increasingly difficult for Russian units to press on when they are sustaining high casualty rates.