The decree, published Thursday on a government website, came after members of the political opposition issued a report saying that at least 220 serving Russian soldiers had died in Ukraine since last spring. That report includes details gathered by the opposition leader Boris Y. Nemtsov, who was killed on a Moscow street in February.

Witnesses have described secret nighttime burials illuminated by truck headlights. Relatives of dead soldiers have told journalists about confusion over whether their loved ones died in training accidents in southern Russia or in combat in Ukraine.

Caught between a desire to honor its soldiers and a need to maintain secrecy in an earlier phase of the Ukraine conflict, the annexation of Crimea, the Kremlin has wavered. At first, it denied any Russian military role in Crimea, where soldiers in ski masks and uniforms with no insignia mysteriously appeared in March 2014 and helped expel the Ukrainian government from the peninsula. Later, the Kremlin acknowledged that the soldiers were Russian troops and even created a holiday in their honor.

When the conflict moved east the next month to Donetsk and Luhansk, two primarily Russian-speaking regions of Ukraine near the Russian border, Russian officials once again denied any involvement, but those denials have evoked broad skepticism.

The Ukrainian military captured two men this month who were wounded in a firefight in the Luhansk region. In videos recorded in a Ukrainian military hospital, the two said they were Russian soldiers ordered to serve tours in Ukraine.

The Russian Defense Ministry acknowledged that both men had served in the Russian Army but denied that they were on active duty at the time of their capture.

Russian soldiers have previously described signing pro forma letters of resignation from the military before crossing the border to fight in Ukraine, while continuing to operate as members of Russian military units.

The United Nations says that more than 6,000 soldiers and civilians have died in the fighting in Ukraine. The United States and other Western governments say there is no doubt that Russia is fueling the fire by sending men and weapons to assist the rebels.