Russia launched one of its largest drone attacks in weeks against Ukraine on Monday night and Tuesday morning, firing nearly 400 long-range drones along with 23 cruise missiles and seven ballistic missiles, according to Ukrainian military officials.

The massive barrage killed four people and injured at least 27, Ukrainian authorities reported. The attack hit at least 10 locations across the country, with dozens of drones continuing to target the capital Kyiv during daylight hours on Tuesday. In one incident, rescue workers responded to a residential building fire in Zaporizhzhia following a drone strike.

The aerial assault coincided with intensified Russian ground operations along the 1,250-kilometer front line in eastern and southern Ukraine. General Oleksandr Syrskyi, Commander-in-Chief of Ukraine's armed forces, said Russian forces launched 619 attacks over four days in simultaneous attempts to break through defensive lines in several strategic areas.

"Fierce fighting unfolded along the entire line of contact," Syrskyi said on Telegram, noting that Russia was bringing up new units and preparing continued attacks. Ukrainian forces have deployed reinforcements to counter the assaults.

The Washington-based Institute for the Study of War assessed that Russia's spring-summer offensive is now underway, citing the escalated strikes since March 17 and movement of heavy equipment and additional troops to front-line positions. Russia has historically intensified its grinding war of attrition as weather conditions improve each year.

Meanwhile, Russian air defenses reported intercepting 55 Ukrainian drones overnight over Russian regions, annexed Crimea, and the Black Sea. The conflict, now in its fifth year since Russia's full-scale invasion, has seen Russia occupy approximately 20% of Ukrainian territory, including Crimea which it seized in 2014.