Heavily armed Al-Shabaab militants stormed an African Union (AU) base in Somalia on Tuesday, triggering a fierce firefight that caused an unknown number of casualties, a local military commander and witnesses said. AU forces dispatched helicopter gunships after the pre-dawn car bomb and gun attack on a camp housing Burundian peacekeepers near Ceel Baraf, a village about 160 kilometres (100 miles) northeast of the capital Mogadishu, the sources said. “There was heavy fighting and casualties inflicted on both sides, but we don’t have more details about this incident so far,” local military comma…