(Reuters) – Ukrainian forces were holding their positions in intense street fighting and under day and night shelling in Sievierodonetsk, officials said, as Russia pushes to control the bombed-out city, key to its objective of controlling eastern Ukraine. FIGHTING * Ukraine’s Security Council Secretary Oleksiy Danilov said on Thursday the situation in Sievierodonetsk was “extremely complicated” and Russian forces were focusing all of their might in the area. “They don’t spare their people, they’re just sending men like cannon fodder … they are shelling our military day and night,” Danilov told…