By Aditi Sangal, Adrienne Vogt, Meg Wagner, Jessie Yeung, Adam Renton, Maureen Chowdhury, Jason Kurtz and Mike Hayes, CNN Russia has ramped up assaults on key Ukrainian cities, as President Zelensky pleads for more international assistance and a second round of talks between Ukraine and Russia are set to take place.The International Criminal Court said it would launch an investigation following Ru