Western and UN leaders have condemned a daylight Russian missile barrage that hit Ukraine’s largest children’s hospital, leaving an unknown number trapped under the rubble, as strikes across the country killed 36 people in one of the deadliest attacks this year. Volodymyr Zelenskiy vowed retaliation as he said Kyiv’s Okhmatdyt hospital, the main treatment centre in the country for children with cancer, had taken a direct missile hit. The strike was part of one of the heaviest attacks on the capital since Russia’s February 2022 invasion. “Russia cannot help but know where its missiles are flying, and must fully answer for all its crimes: against people, against children, against humanity in general,” Zelenskiy posted on the Telegram messaging app. A spokesperson for António Guterres, the UN secretary general, said he strongly condemned the “particularly shocking” strikes against the children’s hospital and another medical facility, and the security council is to meet on Tuesday at the request of Britain, France, Ecuador, Slovenia and the US. Barbara Woodward, the UK ambassador to the UN, said on X: “We will call out Russia’s cowardly and depraved attack on the hospital.” The Italian foreign minister, Antonio Tajani, called the missile strike “war crimes”. The British prime minister, Keir Starmer, condemned “attacking innocent children” as the “most depraved of actions”. The strikes across Ukraine on Monday highlighted the country’s air defence vulnerabilities a day before Nato leaders are set to meet in Washington for their annual summit, where they are expected to announce new measures to aid Ukraine. Twenty-two people were killed in the capital, including two staff members at the hospital, where three children were hurt. The strike largely destroyed the hospital’s toxicology ward, where children with severe kidney issues were being treated. Hundreds of rescue workers and volunteers joined the effort to clear the debris and search for survivors. Officials and emergency staff said it was not immediately clear how many doctors and patients – dead or alive – remained trapped under the rubble. “We are extracting whoever we can. We don’t know the number of people trapped there,” said the health minister, Viktor Liashko, outside the hospital. Images from inside the hospital, which treats 20,000 children annually, showed bloodied children, collapsed ceilings and destroyed operating rooms. Maria Soloshenko, 21, a nurse in the toxicology ward, said hospital staff had been in the process of moving the children to a bomb shelter when the explosion occurred. “There was immediate panic when the strike hit,” she said, her gloves covered in blood. Soloshenko said children as young as 18 months had to be urgently taken off dialysis and quickly evacuated through the building’s windows. The Guardian witnessed many young cancer patients in distress during the evacuation, some barely clothed and with medical tubes still attached to them. Tanya Lapshina, a nurse in the trauma department, where the facade was ripped off by the blast, said they managed to move all the children to a bomb shelter. She said: “It was complete chaos. The children were in panic, crying in the bunker. There are no words for this. It is awful. I am still shaking.” Ukraine’s presidential office published an image showing one child with a head injury. Kyiv’s mayor, Vitali Klitschko, described the attack on the capital as one of the heaviest since Russia’s invasion began more than two years ago. Thanks to western-supplied defences, the city had experienced a relatively peaceful period before Monday. Russia, which has targeted civilian infrastructure throughout the war, denied responsibility for deaths on Monday. In a statement, the defence ministry attributed the incident, without directly referencing the hospital blast, to Ukrainian anti-aircraft missiles, despite visual evidence that appeared to point to a Russian strike. Andriy Yermak, the head of the Ukrainian president’s office, shared an image on X that appeared to show a Russian missile over Kyiv moments before it struck a hospital, identifying it as a Kh-101 cruise missile. Ukraine’s Security Service said it found wreckage from the cruise missile, which flies low to avoid detection by radar, at the site. The Ukrainian prosecutor general, Andriy Kostin, said he had discussed the attack with the international criminal court (ICC) prosecutor, Karim Khan. “We are sending all information and evidence about attacks on Kyiv and other Ukrainian cities to the ICC prosecutor’s office,” he said on national television. The court last month issued arrest warrants for Russia’s former defence minister and its military chief of staff over attacks on Ukraine’s electricity network. The search efforts at the hospital were hindered by air-raid alarms that forced emergency staff to take shelter. Shortly after the strike on the children’s hospital, missile debris fell on a separate medical centre in the Dniprovsky district of the city, the mayor said, with seven people thought to be killed. Strikes were also reported in other parts of the country. In Kryvyi Rih, Zelenskiy’s home town, 11 people were killed and 31 were injured, said Oleksandr Vilkul, the mayor. Another four people died in Pokrovsk in eastern Ukraine when missiles hit an industrial facility, said the Donetsk regional governor. In total at least 36 people across the country were killed, Ukrainian officials said. Zelenskiy said 40 missiles were used in the attack. The International Rescue Committee said the attack was part of a broader pattern of Russian strikes on medical facilities since the invasion. “Since the beginning of the full-scale invasion, the WHO [World Health Organization] has recorded nearly 1,700 attacks on healthcare facilities in Ukraine,” the organisation said in a statement. During a press conference in Warsaw after a meeting with the Polish prime minister, Donald Tusk, Zelenskiy urged Kyiv’s allies to make a decisive response to the attack. “I would also like to hear from our partners [about] a greater resilience and a strong response to the blow that Russia has once again dealt to our people, to our land, to our children,” he said, adding that he was waiting for concrete steps from the west to strengthen Ukraine’s air defences and protect its energy sector.