Russia missile strikes against Ukraine damaged the main children's hospital in Kyiv and killed at least 36 people across the country on Monday during the deadliest wave of air attacks in months.
The daylight attack on the Ohmatdyt Children's Hospital left parents dazed and sobbing as they held their babies outside, Reuters reported.
"It was scary. I couldn't breathe, I was trying to cover (my baby). I was trying to cover him with this cloth so that he could breathe," Svitlana Kravchenko, 33, said.
A photo posted on social media by Ukrainian President Volodymyr Zelenskyy showed a woman holding a bloody baby while apparently surrounded by hospital workers, including a man with blood on his face and neck.
During a news conference in Poland, where he and Polish Prime Minister Donald Tusk signed a military pact, Zelenskyy vowed to strike back at Russia.
"We will retaliate against these people, we will deliver a powerful response from our side to Russia, for sure. The question to our partners is: can they respond?" he said.
The United Nations Security Council plans to meet Tuesday at the request of Britain, France, Ecuador, Slovenia and the United States, Reuters said, citing unidentified diplomats.
Ukraine's prosecutor general said he discussed the attacks with International Criminal Court Prosecutor Karim Khan, and said his office would share evidence with the ICC.
Russia's Defense Ministry, which has repeatedly denied targeting civilians and civilian infrastructure, acknowledged carrying out strikes against what it called defense industry targets and aviation bases in Ukraine, Reuters said.
The death toll in Kyiv was 22, including two children, with 82 wounded during attacks that came two hours apart, Reuters said.
Eleven people were killed and 64 wounded in the Dnipropetrovsk region and three were killed when missiles hit an industrial building in the eastern town of Pokrovsk.
The Ukrainian government declared that Tuesday would be a national day of mourning for the victims.
A video posted online showed a missile falling from the sky toward the children's hospital, followed by a large explosion, Reuters said.
The Security Service of Ukraine identified the weapon as a Russian Kh-101 cruise missile and a Ukrainian air force spokesperson, Col. Yuri Ignat, said the missiles that struck Monday flew at extremely low altitudes.
Kyiv Mayor Vitali Klitschko said Monday's attack was one of the largest of the war, with damage reported in seven districts across the city, and power company DTEK said three three electricity substations and networks were damaged.