In 36 days of fighting on Iwo Jima during World War II, nearly 7,000 Marines were killed. Now, 20 days after President Vladimir V. Putin of Russia invaded Ukraine, his military has already lost more soldiers, according to American intelligence estimates.

The conservative side of the estimate, at more than 7,000 Russian troop deaths, is greater than the number of American troops killed over 20 years in Iraq and Afghanistan combined.

It is a staggering number amassed in just three weeks of fighting, American officials say, with implications for the combat effectiveness of Russian units, including soldiers in tank formations. Pentagon officials say a 10 percent casualty rate, including dead and wounded, for a single unit renders it unable to carry out combat-related tasks.

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With more than 150,000 Russian troops now involved in the war in Ukraine, Russian casualties, when including the estimated 14,000 to 21,000 injured, are near that level. And the Russian military has also lost at least three generals in the fight, according to Ukrainian, NATO and Russian officials.

Pentagon officials say that a high, and rising, number of war dead can destroy the will to continue fighting. The result, they say, has shown up in intelligence reports that senior officials in the Biden administration read every day: One recent report focused on low morale among Russian troops and described soldiers just parking their vehicles and walking off into the woods.

Read more: NY Times