Russian warships patrol Crimea’s coasts and Russian warplanes fly from its territory, transformed by eight years of occupation into a fortress. President Vladimir Putin of Russia has called Crimea a "sacred place,” Russia’s "holy land,” and one of his top advisers has warned that if the peninsula were attacked, Ukraine would face "Judgment Day.”

But lately, Ukraine has been calling the Kremlin’s bluff. Huge explosions rocked a temporary Russian ammunition depot in Crimea on Tuesday, in the latest in a series of clandestine Ukrainian assaults against the Black Sea peninsula that Putin illegally annexed in 2014, and that is now being used as a vital staging ground for Russia’s invasion.

A senior Ukrainian official, speaking on the condition of anonymity to discuss the operation, said that an elite Ukrainian military unit operating behind enemy lines was responsible for the blasts. Russia’s Defense Ministry said in a statement that the episode was an "act of sabotage,” a significant acknowledgment that the war is spreading to what the Kremlin considers Russian territory.