Some 600,000 Soviet troops were killed while fighting the German army on Polish soil.

Poland’s foreign minister said Friday that “security regulations” were behind the decision to ban pro-Kremlin Russian bikers from riding through Poland as they mark the anniversary of the end of World War II.

It is Poland’s second such ban on the nationalistic Night Wolves club. The ban in April 2015 came amid tension between Warsaw and Moscow over Russia’s actions in Ukraine. Poland called the ride a provocation.

Bilateral relations have deteriorated further after a right-wing government distrustful of Moscow took power in Poland in the fall.

In Moscow, Russia’s Foreign Ministry said it had summoned Poland’s ambassador, Katarzyna Pelczynska-Nalecz, to protest this “particularly cynical and malicious gesture aimed at deliberate deterioration in Russian-Polish relations. “

It said the ban deprived Russian citizens of the possibility to “pay tribute to Soviet soldiers who died during the liberation of Europe from fascism.”

Polish Foreign Minister Witold Waszczykowski said that the bikers were refused entry into Poland due to security concerns. He did not elaborate. Ministry spokesman Artur Dmochowski said the decision was dictated by the need to assure public order, and added that Russia’s actions are aimed at discrediting Poland.

The bikers were planning to pass through Poland on their way from Moscow to Berlin to commemorate the Russian Red Army’s and Allied defeat of Nazi Germany 71 years ago. Following the ban in 2015, the bikers took routes bypassing Poland.

An organization of Polish bikers that stays in touch with the Night Wolves said the Russians were planning to visit Red Army war cemeteries in Warsaw and Wroclaw and the former Nazi German death camp of Auschwitz, where thousands of Russian prisoners of war were among the victims.

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