At least three people have been killed and another 17 injured in the biggest Russian drone attack on Ukraine's Kharkiv, the city's mayor saysIhor Terekhov says Russia launched 48 drones, two missiles and four gliding bombs towards the city overnightThere is "a lot of damage" with three high-rise residential buildings hit, he saysIntense strikes across Ukraine happened the previous night, when six people were killed and 80 injuredIt follows Ukraine's major drone attack on Russian airfields last Sunday, which Russian President Vladimir Putin later said he would need to respond to Biggest Russian drone strike hits Ukraine's second city