Russia has threatened Poland with "most serious consequences" for pulling down a monument to a Soviet World War II general.
The removal of the memorial to General Ivan Chernyakhovsky began on September 17 in the northern town of Pieniezno, where the general died of wounds in 1945.
Local authorities argue he symbolizes the foisting of communism on Poland.
For Russia, Chernyakhovsky is a national hero.
Russia's embassy in Warsaw on September 18 issued a statement saying that Russia had "warned the Polish side many times" that removing such monuments "may not remain without the most serious consequences."
Relations between Warsaw and Moscow are already strained in large part over the conflict in eastern Ukraine, where pro-Russian insurgents are waging a separatist struggle.
Poland has been one of Russia's toughest critics since the Kremlin forcibly annexed the Black Sea peninsula of Crimea from Ukraine in March, 2014.
Like other Western countries and Kyiv, Warsaw accuses Moscow of directly supporting the rebels in eastern Ukraine, something Russia denies.