Russia pounded Ukraine with missile and drone attacks overnight on Saturday and into Sunday morning, focusing on the major western city of Lviv.
Ukraine's neighbour Poland scrambled fighter jets in order to ensure the safety of Polish airspace, the Polish military confirmed. Allied NATO aircraft were also deployed.
Lviv's regional head Maksym Kozytskyi reported that two individuals were killed during these strikes, while two others were injured.
Elsewhere, Russia continued to target Ukraine's power plants, with one struck in an overnight attack in Zaporizhzhia, claiming the life of one person and leaving more than 73,000 people without electricity.
The Russian assaults followed a recent statement from a US official supporting Ukraine's capacity to launch deep strikes into Russian territory.
Poland's operational command indicated that Polish and allied aircraft were actively operating in their airspace, bolstered by ground-based air defense and radar reconnaissance systems placed on high alert.
All of Ukraine was placed under air raid alerts as of 05:10 (02:10 GMT) following warnings from the Ukrainian Air Force about imminent Russian missile and drone attacks.
Lviv's mayor Andriy Sadovyi reported that parts of the city, merely 70 km (43 miles) from the Polish border, lost power as air defense systems engaged in repelling attacks.
As of the morning hours, various areas in Ukraine were without electricity, and public transport was also disrupted, with warnings issued about the dangers of venturing outside during these tense times.
The strikes formed a part of Russia's broader threats aimed at Ukraine, with a significant increase in aggression towards its energy infrastructure.
In response, Lithuania briefly closed its airspace due to unidentified objects spotted nearby.
