Search operations were called off at the building, struck on Thursday during Russia's heaviest bombardment of the Ukrainian capital so far in 2026.
"Ukraine will not allow any of the aggressor's strikes that take the lives of our people to go unpunished," Zelenskiy said on Friday after meeting top military and intelligence officials to discuss retaliatory long-range strikes.
Zelenskiy said later in his nightly video address that retaliatory actions had already been approved. He pointed to an overnight strike on an oil refinery that the military said triggered a large fire in the central Russian city of Ryazan.
"Last night, the enemy already saw hits, including on their oil facilities and military facilities," he said.
"We are continuing the operations."
Four people were killed in the Ryazan strike that damaged high-rise apartment buildings, the governor of Russia's Ryazan region said.
Zelenskiy had earlier laid flowers and spoken to rescue workers at the site of the attack in Kyiv's Darnytskyi district, on the left bank of the Dnipro River.
Russia, which began its full-scale invasion of Ukraine in February 2022, had launched more than 1500 drones and dozens of missiles at targets in Ukraine over two consecutive days, according to Ukrainian officials. Six people were also killed in western Ukraine, far from the front line.
Moscow's Defence Ministry said its forces had carried out massive strikes on Ukraine on Tuesday through Friday, the Russian state news agency RIA reported.
Kyiv officials declared Friday a day of mourning, with flags at half-mast across the city of three million.
Entertainment events were cancelled or postponed. Residents brought flowers, stuffed animals and sweets to a makeshift memorial at the destroyed housing block.
Ukraine's Interior Ministry said hundreds of rescuers had sifted through 3000 cubic metres of rubble. Officials said 24 bodies had been recovered and about 30 people rescued alive.
Zelenskiy said initial analysis showed the building had been hit by a recently made Russian Kh-101 missile.
Moscow denies deliberately targeting civilians but during more than four years of war has frequently hit residential buildings and other civilian infrastructure all over Ukraine.
Aboard Air Force One on his way back from China, US President Donald Trump told reporters the strikes on the Ukrainian capital, launched hours after a three-day US-brokered ceasefire expired, could disrupt efforts to find a diplomatic resolution to the war.
