Ukrainian President Volodymyr Zelensky vowed to wreak "wrath" against Russian forces in 2024, hours before Ukraine saw attacks on the first day of the new year.
Russia and Ukraine have seen an escalation in strikes in recent days, including unprecedented strikes on the Russian city of Belgorod that killed 24 people on Saturday.
The attack came a day after Moscow launched a barrage of missiles and drones at Ukrainian cities, killing 39 people, one of the largest aerial attacks since the war began.
Jan. 1 was declared a day of mourning in Ukraine's capital Kyiv, where 19 people had been killed, city officials said.
Just hours after midnight on New Year's Day, the Russian-installed head of the occupied Donetsk region said four people had been killed and 13 wounded by a rocket attack on its main city.
In Ukraine's southern Odesa region, governor Oleg Kiper said one person died in a Russian drone strike, and three others were injured.
And in western Ukraine's Lviv region, air defense systems shot down Russian drones in the early hours, according to governor Maksym Kozytskyi.
Zelensky's televised New Year's Eve address featured clips of Ukrainian artillery and fighter jets.
"Next year, the enemy will feel the wrath of domestic production," he said.
Ukraine will boast at least "a million" additional drones in its arsenal next year, Zelensky added, as well as F-16 fighter jets delivered by its Western partners.
"Our pilots are already mastering F-16 jets, and we will definitely see them in our skies," he said.
Despite billions of dollars worth of Western weapons, Ukraine last year struggled to make a major breakthrough in its counteroffensive against invading Russian forces.
Moscow has meanwhile ramped up pressure along the front lines, capturing the eastern town of Marinka earlier in December and pushing for control of Kupiansk in the northeast.
Kyiv is urging Western allies to maintain military support.
Britain announced it would send hundreds more air defense missiles to Ukraine after Prime Minister Rishi Sunak declared that his country would "continue to stand with Ukraine for as long as it takes."
Zelensky's counterpart President Vladimir Putin did not mention Ukraine in his traditional New Year's Eve address on Sunday, but praised Russia's soldiers on the front line and called for unity in the face of "difficult tasks."
