By Sergiy Karazy and Natalia Zinets IRPIN, Ukraine (Reuters) – Russian firefighters battled a blaze at one of Russia’s main logistics hubs for its Ukraine war effort on Friday, after what Moscow described as a cross-border air raid by Ukrainian helicopters, the first of its kind in the five week war. Ukraine denied responsibility for the huge fire at the fuel depot in Belgorod, a Russian city near the border. Security camera footage of the depot, from a location verified by Reuters, showed a flash from what appears to be a missile fired from low altitude in the sky, followed by an explosion on…