President Volodymyr Zelenskiy promised retribution against Russia on Friday after laying red roses at the rubble of a Kyiv apartment building where a Russian missile strike killed 24 people, including three children.

Aboard Air Force One on his way back from China, U.S. President Donald Trump told reporters that the strikes on the Ukrainian capital, launched hours after a three-day U.S.-brokered ceasefire expired, could disrupt efforts to find a diplomatic resolution to the war.

Search operations were called off at the building, struck on Thursday during Russia’s heaviest bombardment of the Ukrainian capital this year.

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

Kyiv Survivor Saw ‘Flames and an Abyss’

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 1,500 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 May 12-15, the Russian state news agency RIA reported.

“When we opened the front door, we saw flames and an abyss. Half the staircase and the apartment across the hall were completely gone,” Oksana Honcharenko, 57, told Reuters. “We survived, but this pain is indescribable – it’s heartbreaking.”

She added: “We didn’t do anything to deserve this – why are our little children dying? We all pray and ask so much for this horror to end.”

Kyiv officials declared Friday a day of mourning, with flags at half-mast across the city of 3 million.

Entertainment events were cancelled or postponed. Residents brought flowers, stuffed animals and sweets to a makeshift memorial at the destroyed housing block.

About 20 Western diplomats came to show solidarity.

“It demonstrates again that they are definitely not interested in any kind of peace discussions right now,” said French Ambassador Gael Veyssiere.

Ukraine’s Interior Ministry said hundreds of rescuers had sifted through 3,000 cubic meters of rubble. Officials said 24 bodies had been recovered and about 30 people rescued alive.

“My friend lived on the second floor. They found her around 7 p.m. – I don’t remember exactly – along with her husband,” said Tetiana Prudyus, 34, who had brought red roses and was holding back tears.

“I want to say one thing,” she said. “Even after this, we won’t surrender. We’re a very strong nation.”

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.

(Reporting by Olena Harmash; Editing by Daniel Flynn, Kevin Liffey, Ron Popeski and Rosalba O’Brien)