In a speech marking the country's Day of Remembrance, the Russian leader rejected claims that "state interests" provided justification for the government's actions, the Russian news agency ITAR-TASS reported.
"I am convinced that no development of the country, no successes and ambitions can be achieved at the expense of human grief and losses," he said.
Medvedev said it is important for young people to know about what he called "one of the greatest tragedies in Russian history."
In the 1920s and 1930s, 52 million people were sentenced for political reasons, six million were exiled and one million were executed, the latest data shows.
Remembrance Day was instituted in Russia in 1991 after the fall of the Soviet Union.