Instead, Moscow and Kyiv have been drawn into an escalating duel of long-range aerial strikes as fighting along the roughly 1,250-kilometer (780-mile) front line in eastern and southern Ukraine has slowed, restricted by large numbers of drones and ground robots threatening troop movements.

Russia’s parliamentary election for the first time is being held in Ukraine’s regions that Moscow illegally annexed after the start of its full-scale invasion more than 4 1/2 years ago.