As hundreds of supporters queued in Red Square to lay flowers at the grave of the Soviet dictator Joseph Stalin, on the 66th anniversary of his death this week, two young activists mingled with the crowd beneath the Kremlin’s walls.

“Burn in hell, executioner of the people and murderer of women and children!” shouted Yevgeny Suchkov, before snapping a red carnation and hurling it at a granite bust of Stalin. Police and Kremlin security officers reacted instantly, seizing him in a neck lock and dragging him away.

Stalin’s reputation has soared in Russia since Vladimir Putin, a former KGB officer, came to power in 2000. Busts and portraits of the Soviet dictator, once taboo, have reappeared across the country in recent years.

The decommunisation movement, of which Suchov is a member, by contrast wants to see reminders of the Soviet era removed from Russia’s streets, as well as state archives relating to Stalin’s campaign of political terror being opened to the public.

While all the attention was on Suchkov, his fellow activist, Olga Savchenko, stepped up to Stalin’s grave and calmly said: “Shame on the executioner.” She was also detained.

Suchkov, 21, said he had felt obliged to stage his protest because standing by and doing nothing in the face of an “homage to evil” would make him an accessory.

“And I have no intention of becoming an accessory to the evil that was Stalin and Stalinism,” he told the Guardian after his release from police custody. Savchenko, 25, said her great-grandfather was executed by the Soviet secret police in 1937 at the height of Stalin’s purges.

Both activists were ordered to pay a small fine, although they said police had not specified in their report exactly what offence they had been charged with.

A Ukrainian nationalist holds a poster in front of the Russian embassy in Kiev showing Putin and Stalin. Photograph: Sergei Supinsky/AFP

Almost three decades on from the collapse of the communist system in Russia, thousands of metro stations, streets and squares across the country continue to bear the name of Soviet leaders and officials, while almost every town or city has a statue of Vladimir Lenin. Opinion polls indicate around 25% of Russians believe Stalin’s campaign of political terror, estimated to have killed some 20 million people, was “historically justified”.

Critics accused the decommunisation movement of enflaming dangerous social tensions. “We must clamp down hard on this or tomorrow blood will flow across the whole country,” said Alexander Yushchenko, a Communist Party MP.

Knowledge about the Stalin era is patchy among young Russians. There is nothing in the official school curriculum about Stalinist terror, and children can go through their entire school years without hearing anything about the topic. Unsurprisingly, almost half of all Russians aged 18-24 know nothing at all about Stalin’s purges, according to an opinion poll published last year.

Ukraine implemented a decommunisation programme after protests overthrew the country’s pro-Moscow president in 2014. Hundreds of Soviet-era statues and monuments have since been toppled in the parts of the country under government control.

“There is no other method of overcoming the Soviet legacy,” said Alexander Polozun, a 20-year-old decommunisation activist.