BAGHDAD, Iraq — A U.S. Marine helicopter transporting troops to western Iraq crashed Wednesday in the western desert, the U.S. military said. A U.S. spokesman said there were casualties but gave no figures. A Pentagon source said the helicopter was a CH-53 Sea Stallion, which is normally configured to carry 37 passengers, but can take up to 55. There was no immediate word on how many people were on board.ABC-TV and CNN reported that 31 people were killed. MSNBC reported more than 30 dead. The Pentagon would not confirm the casualty count to The Associated Press.The helicopter went down about 1:20 a.m. near the town of Rutbah, about 220 miles west of Baghdad, while conducting security operations, the military said in a statement. The aircraft was transporting personnel from the 1st Marine Division.A search and rescue team has reached the site and an investigation into what caused the crash is underway, the military said."We can confirm casualties, but not what type or numbers yet," a U.S. spokesman, Lt. Col. Steven Boylan, said.