Historians "shocked" by the materials submitted for their scrutiny
Russia's NTV said the three-volume collection of unabridged documents stored at the Lubyanka spy HQ contains "sensational material on abuses of power at the highest levels".
The documents are stamped "for Stalin's eyes only" and "destroy after reading".
Shocking
Most of them were written by the forerunners of the KGB, the CheKa and the GPU, between 1917 and 1934, and will "change ideas about Soviet history", the TV said.
"The summaries of the Cheka agents are more like confessions, and mercilessly expose the regime they themselves created," it said.
"Paragraph after paragraph describe abuses in the army and in the Communist Party, as well as the immoral conduct of Communists and Komsomol (Young Communist League) members."
"The historians themselves seem to be shocked by the materials that they have been allowed to study," according to NTV.
Alongside the secret memoranda addressed to Stalin, the material includes official announcements and Pravda front-page articles of the same period, which shed light on discrepancies between accounts of events in secret police reports and the official propaganda peddled by the country's leaders.
In a hurry
The publication of the records has been rushed through by the Russian history research institute, with the assistance of the current secret service, the Federal Security Service.
Institute head Andrey Sakharov told NTV there had been "a great rush" to submit the documents for public scrutiny, for fear "permission might be withdrawn at the very last moment".
"We did not rule out that someone might want to interfere with the process and hamper the truth from coming out," he said.
Material from the 1937-39 "Great Terror" period when millions of people, including artists and intellectuals, were arrested as "enemies of the people", remain classified for now.
"Perhaps there are too many historical contradictions and things that are difficult to explain there," the TV commented.
A bit of history
Under communism, the secret police changed its name at least eight times. It started after the 1917 October Revolution as the Cheka (the Extraordinary Committee Against Sabotage and Counter-Revolution) tasked with investigating "counterrevolutionary" crimes.
Under Stalin, the secret police, based in Moscow's central Lubyanka square, acquired vast punitive powers.
No one knows exactly how many people were sent to the camps during Stalin's purges, but Russian historian Dmitriy Volkogonov estimates that between four and five million people were detained at any one time in both before and after World War II.