A light aircraft contracted by the United States Government to spray drug crops has crashed in Colombia killing the American pilot on board.
Colombia produces most of the cocaine in the world
A US embassy official said it was not clear whether the T-65 aircraft was shot down by Marxist rebels or crashed accidentally.
Two other US-contracted light aircraft have crashed since February fuelling speculation that the incidents are related to its involvement in the country.
The US has contributed $2bn to Colombia's fight against cocaine and leftist rebels.
Monday's crash occurred in the Narino state in south-west Columbia where there are large plantations of coca - the raw ingredient of cocaine.
String of crashes
On 13 February a US Government Cessna came down in mountains in the south of the country while searching for coco leaf.
Marxist rebels killed a US contractor and Colombian army sergeant on board and took the three other American passengers hostage.
Two weeks ago, another Cessna crashed into the mountain - killing three Americans hired to search for the US hostages.
Rebels and their paramilitary rivals oversee cocaine production in Colombia.
The US crop-fumigating missions are at risk, as they fly close to the ground and are often hit by bullets.
Colombian troops sometimes have a ground presence to protect the spray planes.
But it is impossible to remove every threat.
Meanwhile, Colombian troops assisted by Americans continue to search for the three US hostages.
The Revolutionary Armed Forces of Colombia (FARC) have said they want to trade the men for rebels held in state prisons.