When Russia seized Crimea in 2014, President Vladimir Putin was so worried about Russian casualty figures coming to light that authorities accosted journalists who tried to cover funerals of some of the 400 troops killed during that one-month campaign.

But Moscow may be losing that many soldiers daily in Putin’s latest invasion of Ukraine, American and European officials said. The mounting toll for Russian troops exposes a potential weakness for the Russian president at a time when he is still claiming, publicly, that he is engaged only in a limited military operation in Ukraine’s separatist east.

No one can say with certainty just how many Russian troops have died since last Thursday, when they began what is turning into a long march to Kyiv, the capital. Some Russian units have put down their arms and refused to fight, the Pentagon said Tuesday. Major Ukrainian cities have withstood the onslaught thus far.