Three agents of the U.S. Drug Enforcement Administration in Afghanistan to combat that nation's poppy production which provides much of the world's heroin were among the ten Americans killed when their helicopter crashed following a firefight.

The DEA casualties were the first for the agency since its agents began anti-narcotics operations in 2005.

The DEA issued a statement:

"Today, the Drug Enforcement Administration mourns the tragic loss of three DEA Special Agents and seven U.S. service members killed in a helicopter crash in Afghanistan," said Acting Administrator Michele M. Leonhart. "The incident occurred during the early morning hours of October 26, when these heroic individuals were returning from a completed, joint counternarcotics mission."

"We are all saddened by this tragic event. DEA is an extremely tight family, and the death of these three brave agents is a devastating loss for us. No expressions of grief can adequately convey the depth of the collective sorrow that we feel for their loved ones."

"Our thoughts and prayers are with the family members of our fallen heroes. We owe them a debt of gratitude that can never be repaid and we will forever carry their memories in our hearts."

Besides the DEA agents, who weren't identified, the others killed during this particular operation were uniformed members of the U.S. military, according to U.S. officials.

Officials said the aircraft wasn't taking hostile fire at the time of the crash so they dismissed that as a possibility. The 10 deaths were among 14 Americans who died in helicopter crashes Monday. Two Marine helicopters crashed in Helmand Province, killing four troops.