Entire sections of Baghdad's embattled Sadr City district have been left nearly abandoned by civilians fleeing a US-led showdown with Shiite militias and seeking aid after facing shortages of food and medicine, humanitarian groups said. The reports Wednesday by the agencies, including the UN children's fund, add to the individual accounts by civilians pouring out of the Sadr City area as clashes intensify. US forces have increased air power and armored patrols in the attempt to cripple Shiite militia influence in Sadr City, a slum of 2.5 million people that serves as the Baghdad base for the Mahdi Army led by anti-American cleric Muqtada al-Sadr. Claire Hajaj, a UNICEF spokeswoman based in Jordan, said up to 150,000 people - including 75,000 children - were isolated in sections of Sadr City "cordoned off by military forces." She said about 6,000 people have been forced to flee their homes and that some areas of southeastern Sadr City were virtually abandoned.