A US helicopter went down after coming under fire Thursday in a Sunni militant stronghold south of Baghdad but there was no immediate word on casualties, an Iraqi army official said. The US military confirmed the report. All nine on board survived but four were wounded. Gunmen opened fire on a Black Hawk helicopter at about 7:30 a.m. as it flew over Latifiyah, 30 kilometers south of Baghdad, the Iraqi official said. The helicopter went down in a rural area and US forces had cordoned off the site, the official said.