KYIV — Four people have been killed and more than 50 others injured in a massive wave of Russian missile and drone strikes on Ukraine's capital Kyiv and its surrounding areas on Sunday, officials said.Explosions reverberated through Kyiv just after 1 a.m. (2200 GMT Saturday), following a warning by Ukraine's air force ‌on its Telegram channel that Russia might launch a hypersonic Oreshnik ballistic missile.Kyiv Mayor Vitali Klitschko said that two people had been killed and 56 others injured in the attacks on the city, with 30 of those hospitalized. Some damage was reported in the city's historic Independence Square.Three children are among the injured, with rescue work under way in all over the capital city.There has not yet been any confirmation of Russia using the missile in its latest bombardment."It was a terrible night for Kyiv," Klitschko said in a Telegram ⁠message from the site of one attack. "Right now, rescuers are putting out fires and clearing debris. Medics are providing assistance to the victims."The strikes follow Russian President Vladimir Putin's vow to retaliate after accusing Ukraine of carrying out a deadly attack on a student dormitory in the town of Starobilsk on Friday in which 18 people were killed.The general staff of Ukraine's armed forces said it did carry out an attack near Starobilsk in Russian-occupied eastern Ukraine overnight on Friday, but maintained that it struck an elite Russian military unit.Many residents sought shelter overnight in the city's metro stations.Nataliia Zvarych, 62, said she had rushed to her local station as explosions started rocking the city."It was terrifying, scary," she said. "We have been sitting here for more than three hours now, listening to the explosions up there."The head of the city's military administration said that more than 40 locations in the city had been damaged.Strikes were reported in other parts of Ukraine. A further two people were killed and nine others injured in attacks on the broader Kyiv region surrounding the capital, said regional governor Mykola Kalashnyk.Emergency services rushed to multiple scenes of damage across the city, putting out blazes, clearing debris and treating the injured.Kalashnyk described the attack as "deliberate terror against peaceful people", adding that "emergency services are working in all places".As the sun rose, black smoke from ‌several fires ⁠drifted across the skyline, leaving an acrid smell in parts of the city. Firefighters used hoses to douse the flames in damaged buildings while rescue workers evacuated the wounded.The facade of one five-story residential building had collapsed, images showed. Officials reported damage to offices, shops, warehouses and the foyer of a metro station.President Volodymyr Zelenskiy had warned on Saturday that Russia was preparing a strike against Ukraine using the ⁠Oreshnik missile, citing intelligence from Ukraine, the US and Europe.Russia has already attacked Ukraine twice with the Oreshnik, a missile with a range of several thousand kilometres and capable of carrying a nuclear warhead.Putin has boasted that Oreshnik is impossible to intercept because of its ⁠reported velocity of more than 10 times the speed of sound.Zelenskiy's warning came after Putin ordered his military to prepare options for retaliation against Ukraine for a drone strike on a student dorm in the Russian-occupied Luhansk region of eastern Ukraine on Friday.