A report containing material compiled by slain Russian opposition leader Boris Nemtsov says at least 220 Russian soldiers died in two battles in eastern Ukraine within the past year.

The Russian Defense Ministry denies that any of its soldiers are fighting in Ukraine, saying that Russians who have joined the separatists are volunteers.

The report, published Tuesday, claims the soldiers were released from their duties and listed as volunteers.

The 64-page report was compiled from witness reports in media accounts and information gathered by Nemtsov, including from relatives and other representatives of the dead soldiers.

Nemtsov was shot dead on Feb. 27 in central Moscow. Five suspects, including a Chechen police officer, were arrested in the killing, but investigators have not named a suspected mastermind and the motive remains unclear.