Russian forces launched hundreds of drones and missiles targeting Ukraine's energy and power plant infrastructure on Sunday.
Explosions were reported in the Ukrianian cities of Kyiv, Odesa, Zaporizhzhia, Kryvyi Rih, Dnipro and in western Ukraine. Odesa, a port city, was reportedly left without power.
Poland's military reacted to the attack by scrambling its own airforce within its borders, though there were no reports of Russian ordnance falling on Polish soil.
Russia has repeatedly targeted Ukraine's energy infrastructure as temperatures get colder in Ukraine, a strategy Mosocw has employed in previous years of the conflict.
The attack comes as President-elect Donald Trump is expected to soon appoint a Ukrainian peace envoy to lead negotiations on ending the war with Russia.
The job is not expected to be a salaried role - from 2017 to 2019, Kurt Volker had served as special representative to Ukrainian negotiations on a volunteer basis.
Trump has been rolling out appointee names of those he wants to fill his Cabinet and advise him on top issues at a lightning-quick pace.
Trump has long insisted he could negotiate an end to the war with Ukrainian President Volodymyr Zelensky and Russian President Vladimir Putin. Few details have been given about how he would do this.
Some advisers are reportedly encouraging Trump to push Kyiv to agree to terms that would freeze the frontlines by creating an 800-mile-long demilitarized zone and allow Russia to keep the land it has illegally seized, which amounts to roughly 20% of Ukraine.
It has also been suggested that Kyiv should agree not to pursue NATO membership for 20 years, a stipulation that critics of this plan argue kowtows to Putin.
Fox News' Morgan Phillips and the Associated Press contributed to this report