(Reuters) – Ukrainian forces are preparing for new Russian attacks on the Donbas region in the southeast after they repelled Russia’s assault on the capital Kyiv, President Volodymyr Zelenskiy said on Thursday. FIGHTING * The southern port city of Mariupol and a “corridor” between two eastern towns, Izyum and Volnovakha, are becoming the key battlefronts, a Ukrainian interior ministry adviser said. * Nearly 5,000 people have been killed in Mariupol, the mayor’s office estimates, and about 170,000 people remain trapped amid ruins without food, heat, power or running water. Many more have fled. …