Hundreds of US and Iraqi forces backed by helicopters and jet fighters attacked and killed 33 Sunni insurgents who were holding back the water supply to the Shi'ite town of Khalis, the American command said in a statement Tuesday. The assault began before dawn on Monday when a joint force was dropped by helicopter in the village of Gubbiya, 15 kilometers east of Khalis. The assault force killed 13 fighters and attack aircraft killed 20 others, the military said. The area is known to be controlled by al-Qaida in Iraq. Khalis, 80 kilometers north of Baghdad, has been the scene of repeated Sunni insurgent bombings and mortar attacks. "The objective of the mission was to open the spillway, which regulates water flow to the town of Khalis, restoring the essential service of water," the statement said. The assault uncovered three weapons caches, led to the capture of three men and "water is currently flowing unimpeded to Khalis," the military said. The statement did not say if any US or Iraqi soldiers were killed or wounded.