Complex sentence: During this time, the Afghan security forces, accompanied by the Russian advisers swarmed the hallway and surrounding rooftops, but negotiations stalled, leading to an intense exchange of cross fire, after Russian advisers ordered an assault.
Split into simpler sentences: During this time, the Afghan security forces, accompanied by the Russian advisers, swarmed the hallway and surrounding rooftops. When negotiations stalled, there was an intense exchange of fire after Russian advisers ordered an assault.