Special report:Tension escalates in Iraq

   BAGHDAD, Feb. 7 (Xinhua) -- The U.S. military confirmed on Wednesday that a CH-46 helicopter went down northwest of Baghdad without releasing information about casualties.

   "We have a CH-46 that is down about 30 km northwest of the capital," U.S. military spokesman Maj. Gen. William Caldwell told reporters, referring to the Chinook transport helicopter.

   "A quick reaction force is on site and the investigation is going on as we speak," he said at a news conference in Baghdad.

   Caldwell refused to elaborate on casualty, saying it is "inappropriate in this stage."

   Witnesses in the area west of the U.S. airbase of Taji, 20 km north of Baghdad, said they saw that a helicopter crashed after it was hit by ground gunfire.

   They also said that U.S. troops cordoned off the scene and started to check the wreckage and six helicopters flew over the area.