KYIV, Ukraine (AP) — A spate of explosions and fires has turned Russian-occupied Crimea from a secure rear base into a new battleground in the war, demonstrating both the Russians' vulnerability and the Ukrainians' capacity to strike deep behind enemy lines.

Nine Russian warplanes were reported destroyed at an air base in Crimea last week, and an ammunition depot on the peninsula blew up on Tuesday.

Ukrainian authorities have stopped short of publicly claiming responsibility, preferring to keep the world guessing, but President Volodymyr Zelenskyy alluded to Ukrainian attacks behind enemy line...