File Photo: An armed man stands by the remains of a Russian military vehicle in Bucha, close to the capital Kyiv, Ukraine, Tuesday, March 1, 2022. AP
This is NATO's first public estimate of Russian casualties since the war started on Feb. 24.
The military officer, speaking on condition of anonymity under ground rules set by NATO, said the estimate of the number killed is based on a combination of information from the Ukrainian government, indications from Russia, and open-source information.
The US government has largely declined to provide public estimates of Russian or Ukrainian casualties, saying available information is of questionable reliability.
The NATO military officer, in a briefing from the alliance's military headquarters in Belgium on Wednesday, said the estimate of 30,000 to 40,000 Russian casualties is derived from what he called a standard calculation that in war an army suffers three wounded soldiers for every soldier killed.
The casualties include killed in action and wounded in action, as well as those taken prisoner or missing in action, the officer said.