Sixteen Colombian police officers have been killed after their helicopter crashed while searching for the nation's most wanted drug lord.
Two other officers were critically injured when the US-made UH-60 Black Hawk came down in a wooded area of north-west Colombia.
The officers were hunting for Dairo Otoniel Usaga, leader of Colombia's most violent drug-smuggling gang.
The area where the helicopter crashed - in dense jungle dominated by drug traffickers and a refuge for leftist rebels - fuelled speculation that the helicopter may have been shot down.
But the country's defence minister said two other helicopters also participating in the mission did not detect any gunfire.
Low-lying cloud likely obstructed the pilot's vision, causing it to crash at 110mph into a hillside, Luis Carlos Villegas added.
The United States is offering a reward of up to $5 million for information leading to the capture of Otoniel, who runs Colombia's most violent drug-smuggling gang.
Since February, efforts to find Otoniel have been stepped up.