Fifteen soldiers were killed and 21 injured in the attack, the deadliest strike against U.S. forces since the war began.
Lt. Col. Thomas Budzyna said some Fort Carson troops were among the injured but he didn't know the units or bases of the others injured or killed. The military does not confirm deaths of soldiers until their families have been notified.
In addition to Fort Carson, some of the troops on the two helicopters, which were taking many of them from duty in Iraq for R&R leave, were from Fort Sill, Okla., Fort Campbell, Ky., and Fort Hood, Texas.
"Many were looking forward to a break in the action," Budzyna said. "Unfortunately, they faced something else."
Fort Hood spokesman Cecil Green said he could not confirm any details.
Col. William Darley, spokesman for the U.S. military in Baghdad, said in an e-mail that the victims apparently were from an assortment of units and he understood some were from medical units.
The attack came on the first day of a stepped-up R&R program, with the number of troops to be increased from approximately 270 a day to 479 per day, according to Central Command.
"When another soldier dies it's like losing a brother," Pvt. Eric Kragan told WSB-TV as he arrived at Hartsfield Atlanta International Airport to start his two-week R&R leave.
"It's hard to be a soldier and hear about somebody dying," said Sgt. Michael Williams, also arriving in Atlanta. "Everything from day to day is a different experience, or a different change. From minute to minute you don't even know what to expect."
Fort Carson has sent 12,000 troops to Iraq — its largest deployment since World War II — including units from the 3rd Armored Cavalry Regiment, 3rd Brigade Combat Team and battalions of the 10th Special Forces Group.
At least 21 soldiers from the post have died in Iraq, all since President Bush declared an end to major combat on May 1.
Soldiers from Fort Carson have been coming back in small numbers for "rest and recuperation" leave, Budzyna said Sunday. A "Welcome Home" banner hung from one of the post's gates, but he couldn't say if any groups were due back this week.
Seeing those returned soldiers in their desert camouflage uniforms is difficult for people whose spouses haven't been granted leave, said Heather Harlan, whose husband is a 3rd Armored Cavalry cook stationed at Al Asad Air base and not scheduled for leave.
"We're planning a Christmas party but we don't even know how many people will show up," Harlan said.
She and her two young daughters plan to visit family in Cheyenne, Wyo., for Thanksgiving because she doesn't want to attend the unit's annual dinner without her husband. "I'm getting as far away from here as possible," she said.