Russian President Vladimir Putin on Friday accused NATO member Poland of having territorial ambitions in the former Soviet Union and said any aggression against Russia’s close ally Belarus would be considered an attack on Russia.

Moscow would react to any aggression against Belarus, which forms a loose Union State with Russia, “with all the means at our disposal,” Putin said.

In his remarks, Putin also stated that the western part of Poland was a gift from Soviet leader Joseph Stalin to the country and that Russia would remind Poles about it.

Polish Prime Minister Mateusz Morawiecki on Friday evening said in a tweet, “Stalin was a war criminal, guilty of the death of hundreds of thousands of Poles. Historical truth is not debatable. The ambassador of the Russian Federation will be summoned to the Ministry of Foreign Affairs.”

Poland denies any territorial ambitions in Belarus.