The fall of the eastern Ukrainian city of Avdiivka to Russia over the weekend was a major symbolic loss for Ukraine and the West. But while American officials initially argued that it was not a significant strategic setback, that calculus could soon change.

My colleagues reported today that hundreds of Ukrainian troops may have disappeared or been captured during Ukraine’s chaotic retreat from Avdiivka. Two soldiers with knowledge of the retreat estimated that 850 to 1,000 troops had been captured or were missing, a range that Western officials said seemed accurate.

The devastating losses could deal a blow to Ukraine’s morale, which has eroded after last year’s failed counteroffensive and the recent removal of a top commander. Officials have said they want to mobilize up to 500,000 more people, but the capture of soldiers could make the effort to recruit them more challenging.

In the U.S., the Biden administration said it was preparing “major sanctions” against Russia in response to the death of the opposition leader Aleksei Navalny.

In Spain, police said the body of Maksim Kuzminov, a Russian pilot who defected to Ukraine, was found riddled with bullets.