WASHINGTON, Jan. 10 (UPI) -- The release of riot-control gas in 2005 from a helicopter and vehicle in Baghdad by the private U.S. security firm Blackwater was a mistake, the company said.

The May 2005 incident came to light recently detailing how at least 10 U.S. soldiers at a checkpoint and an unknown number of civilians were gassed by a Blackwater helicopter and a second time from a Blackwater armored vehicle, The New York Times (NYSE:NYT) reported.

None of the soldiers required medical treatment for exposure to CS gas, which temporarily blinds people, causes skin irritation, coughing and choking, the report said.

Anne Tyrrell, a spokeswoman for Blackwater, told the Times in an e-mail message the attacks were human error by staff.

"Blackwater teams in the air and on the ground were preparing a secure route near a checkpoint to provide passage for a motorcade," Tyrrell wrote. "It seems a CS gas canister was mistaken for a smoke canister and released near an intersection and checkpoint."

The U.S. military can use riot-control gas in a war zone only under the strictest circumstances, which various soldiers said didn't exist that day, the Times said.