Russian President Vladimir Putin has classified deaths of Russian troops in peacetime a state secret.
The move comes as Moscow stands accused of sending soldiers to fight in eastern Ukraine.
Putin has repeatedly denied any involvement of Russian troops in the region.
A report initiated by slain opposition leader Boris Nemtsov and released this month said at least 220 serving Russian soldiers were killed in eastern Ukraine last summer and earlier this year.
In February Ukraine’s President Petro Poroshenko held up passports he claimed belonged to Russian troops in Ukraine.
“This is the best evidence for the agression and the presence of russian troops,” said Poroshenko.
Russia denies intervening directly in the conflict.
Russia annexed Crimea from Ukraine last year after wrestling control over the peninsula by deploying troops with no insignia. Moscow initially vehemently denied they were Russian troops.
Putin only admitted Russian soldiers had been deployed in Crimea nearly one month after completing its annexation.