Ukrainian President Volodymyr Zelenskyy vowed retaliation against Russia on Friday after laying red roses at the ruins of a Kyiv apartment block destroyed in a missile strike that killed 24 people, including three children.

The strike, described by Ukrainian officials as part of the heaviest bombardment of the capital this year, hit a residential building in Kyiv’s Darnytskyi district on Thursday, hours after the expiry of a three-day ceasefire brokered by the United States.

Speaking after meetings with military and intelligence officials, Zelenskyy said Ukraine would respond with long-range strikes against Russian targets.

“Ukraine will not allow any of the aggressor’s strikes that take the lives of our people to go unpunished,” he said.

In his nightly address, Zelenskyy said retaliatory operations had already begun, referring to an overnight Ukrainian strike on an oil refinery in the Russian city of Ryazan, which authorities said caused a large fire and damaged apartment buildings.

“Last night, the enemy already saw hits, including on their oil facilities and military facilities,” Zelenskyy said. “We are continuing the operations.”

Russian regional officials said four people were killed in the Ryazan attack.

Travelling aboard Air Force One after a visit to China, Donald Trump told reporters the strikes on Kyiv could complicate diplomatic efforts aimed at ending the war.

Search operations at the destroyed Kyiv building ended on Friday after emergency crews spent hours clearing thousands of cubic metres of rubble. Ukrainian authorities said around 30 people were rescued alive.

Kyiv observed a day of mourning, with flags lowered across the city and public entertainment events cancelled. Residents gathered near the site to leave flowers, toys and sweets in memory of the victims.

“When we opened the front door, we saw flames and an abyss,” resident Oksana Honcharenko said. “Half the staircase and the apartment across the hall were completely gone.”

“We survived, but this pain is indescribable,” she added. “Why are our little children dying?”

Tetiana Prudyus, whose friends died in the strike, said Ukrainians would not surrender despite the attack.

“Even after this, we won’t surrender. We’re a very strong nation,” she said.

According to Ukrainian officials, Russia launched more than 1,500 drones and dozens of missiles over two days. Six additional deaths were reported in western Ukraine.

Russia’s Defence Ministry said its forces had carried out “massive strikes” against Ukrainian targets between May 12 and 15.

Zelenskyy said preliminary analysis showed the Kyiv building had been struck by a recently manufactured Russian Kh-101 missile.

Moscow denies deliberately targeting civilians, although residential areas and civilian infrastructure across Ukraine have repeatedly been hit since the full-scale invasion began in February 2022.