ADEN/CAIRO, April 26 (Reuters) - Air raids, naval shelling and ground fighting shook Yemen on Sunday in some of the most widespread combat since a Saudi-led alliance intervened last month against Iranian-allied Houthi militia who have seized wide areas of the country. There were at least five air strikes on military positions and an area near the presidential palace compound in the Houthi-held capital Sanaa at dawn on Sunday, while warships pounded an area near the port of the southern city of Aden, residents said. "The explosions were so big they shook the house, waking us and our kids up.