Small, maneuverable and impossible to jam, Russia’s best fiber-optic drones can—in the hands of skilled operators—slip into the buildings and dugouts sheltering Ukrainian vehicles. A video circulated by Russian sources on or before Monday depicts a warhead-laden quadcopter drone easing under a tarp and into a barn where a Ukrainian Bohdana wheeled howitzer was parked.

Several Ukrainian drones were intercepted over Moscow and the surrounding region overnight, with some coming within two miles of the Kremlin, Russian officials said Friday. The attacks, part of an escalating series of strikes on Russian territory,