KINSHASA (Reuters) - United Nations attack helicopters hit rebel positions in eastern Congo on Saturday after insurgents gained ground in heavy fighting with government troops, the U.N. said. The clashes to the south of the town Kibumba mean the rebels have advanced to within 30 km (18 miles) of Goma, the closest they have been to North Kivu's provincial capital since a rebellion exploded in the eastern provinces eight months ago. North Kivu governor Julien Paluku said the army retreated to the southern outskirts of the town after M23 rebels - a group of soldiers who mutinied in April -...