Russian nationalists removed plaques commemorating the execution of 6,000 Polish officers by the Soviet secret police after officials said they were historically inaccurate.
The plaques in Tver, a city 110 miles northeast of Moscow, were installed in the early 1990s by a human rights group on the facade of a former secret police headquarters.
Last year, a prosecutor in Tver ruled that the plaques were “not based on documented facts”.
About 22,000 Polish citizens were allegedly killed by the NKVD, the precursor of the KGB, between April and May 1940. The murders, including those of Tver, became known as Katyn massacre after the forest where the majority of the prisoners were killed.
The Kremlin has insisted for decades that the massacre was perpetrated by the Nazis. Hwever, in 1990 Mikhail Gorbachev, the last Soviet leader, said that Moscow was responsible.
The Russian parliament also issued a statement in 2010 directly accusing Stalin of the murders.
Such a condemnation of the Soviet leader has become rare in Russia since 2014, when tensions with the West increased after the annexation of Crimea to Ukraine.