Southern separatists gained ground across Yemen's second city Aden on Saturday and surrounded the presidential palace amid fierce battles with loyalist forces, military and security sources said. The deadly fighting reflects deep divisions between secessionists and forces backing the internationally recognised government of President Abderabbo Mansour Hadi, experts say. The force, known as the Security Belt, overran three military barracks belonging to unionist forces on Saturday and were surrounding the presidential palace, sources close to the force said.