Russia carried out a large-scale drone and missile attack on civilian areas across Ukraine, killing at least four people and injuring 27 others, officials said Tuesday, amid indications that Moscow may be launching a new spring offensive.

Ukraine’s air force said Russia fired nearly 400 long-range drones overnight in one of the biggest attacks in recent weeks. The assault continued into Tuesday morning, with dozens of drones targeting the capital, Kyiv, even during daylight hours.

In addition, Russia launched 23 cruise missiles and seven ballistic missiles overnight, hitting at least 10 locations across the country.

Ukraine has been facing constant attacks since Russia began its full-scale invasion more than four years ago. Efforts to reach a ceasefire through US-led talks have failed, while the ongoing Iran conflict has shifted global focus away from Ukraine.

Along the roughly 1,250-kilometre front line in eastern and southern Ukraine, Ukrainian forces are preparing for increased attacks as weather conditions improve. Army chief Gen. Oleksandr Syrskyi said Russian troops have recently tried to break through defenses in several key areas.

“Intense fighting is ongoing along the entire front line,” Syrskyi said, adding that Russia launched 619 attacks over four days. He noted that Ukraine has sent reinforcements to counter the assaults.

The Washington-based Institute for the Study of War said recent developments suggest Russia’s spring-summer offensive is already underway, with increased troop deployments and heavier equipment near the front lines.

Despite stepping up attacks, Russia has so far made only limited territorial gains and currently controls about 20% of Ukraine, including Crimea, which it annexed in 2014.

Facing a shortage of troops, Ukraine has relied heavily on advanced drone technology. Kyiv is also seeking to exchange its battlefield drone expertise with Western and Gulf partners for much-needed air defence systems.Meanwhile, Russia said it intercepted 55 Ukrainian drones overnight over its regions, Crimea and the Black Sea.