MOSCOW — Members of Russia’s political opposition published a posthumous report by the politician Boris Y. Nemtsov on Tuesday that documented the deaths of 220 Russian soldiers in the fighting in southeastern Ukraine, even though the Kremlin denies being involved in the war there.

The report, which goes into various clandestine aspects of the war in Ukraine, became particularly noteworthy after Mr. Nemtsov, an opponent of President Vladimir V. Putin, was assassinated in February.

A committee completed the 64-page work, called “Putin. War: According to the Materials of Boris Nemtsov,” which draws on handwritten notes and documents found after the shooting of Mr. Nemtsov, a former deputy prime minister and opposition leader, outside the Kremlin walls. Whether he was targeted for his work on the report is still unclear, and may never be fully known.

Colleagues used the release to praise Mr. Nemtsov and promote the report as shedding new light on the Russian Army’s interventions in Ukraine over the past year.