By Natalia Zinets and Pavel Polityuk LVIV/KYIV, Ukraine (Reuters) – Intense Russian air strikes are turning besieged Mariupol into the “ashes of a dead land”, the city council said on Tuesday, as the United States and Europe planned more sanctions to punish Moscow for its invasion of Ukraine. Street fighting and bombardments raged in Mariupol, Ukrainian officials said, a day after it rejected an ultimatum from Russia to surrender. Hundreds of thousands are believed to be trapped inside buildings, with no access to food, water, power or heat. Russian forces and Russian-backed separatist units h…