Ukraine Faces Russia's Spring Offensive Amid Heavy Drone Strikes
Ukraine's Gen. Syrskyi reported 619 attacks in 4 days, 750-mile front fighting.
Russia fired 23 cruise and 7 ballistic missiles, hitting 10 locations.
Ukrainian forces deployed reinforcements; Russia's air defenses intercepted 55 drones.
Institute for the Study of War says spring-summer offensive is underway, Russia controls 20% of Ukraine.