A museum studying Soviet prison camps has discovered a secret Russian order from 2014 instructing officials to destroy data on prisoners – a move it said “could have catastrophic consequences for studying the history of the camps”.

Up to 17 million people were sent to the Gulag, the notorious Soviet prison camp system, in the 1930s and 1940s. At least 5 million of them were convicted on false testimony. The prison population in the labour camps peaked at 2 million people.

Case files of the Gulag prisoners were often destroyed but their personal data was kept on registration cards, which are still held by police and intelligence officials.

The Gulag History Museum in Moscow has discovered a classified 2014 order that instructed Russian officials to destroy the registration cards of former prisoners who had reached the age of 80 – which today would include almost all of them.

The museum’s archive expert, Alexander Makeyev, told the Interfax agency that they discovered the cards had been destroyed in one region, the remote Magadan in eastern Russia, home to some of the Soviet Union’s biggest prison camps.

Repressions perpetrated under the Soviet dictator Josef Stalin left a profound scar on the Russian nation, destroying lives and displacing millions. But in recent years under Vladimir Putin, officials have tried to play down Stalin’s terror, hailing the leader for building a new economy and helping the Soviet Union win the second world war.

The Gulag History Museum has appealed to Russia’s Presidential Council for Human Rights to look into the classified order.

The report has caused outrage in the Russian historical community and beyond.

Vladimir Zhirinovsky, the leader of the nationalist Liberal Democratic party, said on his social media account that historical “archives should be opened to public, not destroyed” and that Russians should be able to know the truth about their past.