A helicopter on an anti-drugs mission crashed in the Colombian jungle today, killing all 20 Colombian soldiers aboard, the army said.
The Black Hawk transport helicopter went down in bad weather near the town of Magui Payan in the southwestern province of Narino, the army said.
The Colombian troops were on a mission to secure crops of coca - the raw material of cocaine - before spraying planes destroyed them, it said.
It was the worst accident for Colombian military aviation since another Black Hawk crashed in March 2003, killing 23 troops.
The United States provided Black Hawks to Colombia as part of more than $3 billion in mainly military aid since 2000 to tackle the world's largest cocaine industry.
Although the army said the crash was caused by bad weather, Marxist rebels often fire at military helicopters to protect cocaine crops.
Leftist guerrillas and far-right paramilitaries both draw funds from the drug trade as they wage a 40-year-old war which claims thousands of lives a year.