Russia has been accused of interfering in the affairs of the Czech Republic after its embassy tried to block changes to the inscription on a Soviet-era statue.

Russian diplomats say councillors are trying to rewrite history with proposed wording explaining the chequered role of Russian Marshal Ivan Konev, who was twice designated a Hero of the Soviet Union by Stalin and whose remains are buried in the Kremlin. The diplomats have successfully delayed the change after petitioning the mayor, lobbying the foreign and culture ministries, enlisting the support of other former Soviet states and, most recently, invoking an obscure 1985 treaty on the protection of Europe’s architectural heritage.

Now the dispute is set to come to a head at a historically sensitive moment, as the local authority seeks to install the revised inscription by 21 August, the 50th anniversary of the 1968 invasion of then-communist Czechoslovakia by Soviet-led forces to crush the liberal Prague Spring. The new plaque – inscribed in English, Czech and Russian – will assert that Konev was involved in planning the invasion.

The imposing monument in Prague’s affluent Bubeneč district – created by local sculptors in 1980 when Czechoslovakia was a Soviet ally – has been a source of contention and a target for vandals since the communist regime fell in the 1989 Velvet Revolution. After earlier proposals to dismantle the statue or reduce its scale were shelved, attention shifted to its glowing Czech-language inscription, crediting Konev with saving Prague from destruction by Nazi occupying forces in May 1945, when the Red Army liberated much of the country.

Marshal Konev is welcomed by residents in Prague after the city’s liberation from German troops in 1945. Photograph: TASS via Getty Images

Critics said the original plaque, which was removed several weeks ago, exaggerated the marshal’s role while omitting more notorious subsequent actions – including commanding the suppression of the 1956 Hungarian uprising and overseeing the building of the Berlin Wall, besides leading reconnaissance missions for the 1968 invasion.

“The previous plate was actually lying,” said Ondřej Kolář, mayor of the Prague Six municipality, where the monument and Russia’s embassy sit. “When Soviet troops arrived in Prague on 9 May 1945, there was only one SS division here and that was on the outskirts of the city. The Wehrmacht had surrendered to the forces of the Prague uprising, and left the previous day.

“The city was basically free, but that wasn’t something Soviet propaganda wanted to use. We are not denying the role of the Red Army or saying the Soviets didn’t suffer. They suffered a lot – but not in Prague.”

The new engraving credits Konev with commanding forces “who liberated northern, central, and eastern Bohemia” and says they were “the first to enter Prague on 9 May 1945”. It links him with the events in Hungary and Berlin and adds: “In 1968, he personally backed the intelligence surveillance preceding the invasion of the armed forces of the Warsaw Pact into Czechoslovakia.”

The inscription’s accuracy has been endorsed by the Czech army’s Military History Institute and the Academy of Sciences, and by independent local historians. “The words are correct,” said Petr Blažek, a historian with the Prague-based Institute for the Study of Totalitarian Regimes. “Konev’s role in 1945 is generally known – his role in 1968 and 1956 much less so.”

However, it has provoked a furious response from the Russian embassy, which dismissed the connection with 1968 as “unsubstantiated allegations” and said the new inscription “distorts the original monument”.

“The unmistakable change in the appearance of a monument important to preserving the memory of our nation’s heroic struggle against Nazism creates a dangerous precedent,” said Nikolay Bryakin, an embassy spokesman.

Kolář – a member of the pro-EU Top 09 party, who says he has received anonymous threats over the issue – called Russia’s tactics “blackmail” and said they were part of an effort by the government of President Vladimir Putin to influence Czech politics and assert influence over former Soviet satellite states. “What allows the Russian state to tell another sovereign country that is a member of the European Union and Nato what it should or shouldn’t do with its own property? It’s as if we’re their colony,” he said.

But the Russian position is backed by the Czech Communist party (KSČM), which recently reached a deal to keep the current minority Czech coalition government in power.

Josef Skála, a former party vice-chairman, called the inscription change “a dirty game” and added: “Would you be happy if a text appears on the monuments of Winston Churchill, depicting his role in the death of millions of innocent people?”