At least 73 people die during shelling in Mogadishu, adding to a death toll already in the hundreds from this week's battles pitting militias and Islamists against Somali and Ethiopian troops. The escalating war has sent more than 321,000 residents fleeing in the biggest refugee movement in Somalia since the 1991 fall of a dictator ushered in 16 years of anarchy. The week's final death toll is expected to soar and may come close to the estimated 1,000 casualties from a similar four-day flare-up at the end of March. Most of the victims are civilians. Even by Somali standards, Saturday's carnage was shocking. Residents and medical staff interviewed by Reuters confirmed a minimum of 73 casualties from the incessant shelling and gunfire across the city on Saturday, adding to an estimated 131 others from the previous three days' violence. The Islamists ruled most of south Somalia for the second half of 2006, before being defeated in a brief war over the New Year. But their fighters -- backed by some disgruntled Hawiye clan elements -- have regrouped to rise up against President Abdullahi Yusuf's administration and his Ethiopian backers. In the city itself, residents are moving out in big numbers. Many refugees are living under trees and beside roads, short of food, water and any basic amenities. Disease is already spreading. The only operating hospital, Madina, was packed with wounded, screams echoing through the corridors. Tents were set up in the hospital garden to deal with the influx, with many people nursing injuries unattended under trees in the heat. The United States, Ethiopia and Somali government say the rebels are linked to al Qaeda, but Islamist leaders deny that, saying they are being deprived of a say in Somalia's future.