Sixteen Colombian police officers died on Tuesday when their helicopter - US made UH-60 Black Hawk - crashed into the side of mountain in a jungle area in northwestern Colombia, said Defence Minister Luis Carlos Villegas.
Two other uniformed personnel are being treated for serious burns.
"For now the most probable hypothesis is that the helicopter crashed against the side of the mountain, possibly due to low cloud cover," Villegas told reporters in Bogota.
They were participating in a counter-narcotics operation in some 450 km northeast of the capital Bogota for hunting the leader of Colombia’s most wanted drug trafficker Dairo Antonio Usuga David.
The accident came four days after 11 air force personnel died when a Spanish-made CASA C-235 airplane suffered motor failure and crashed near the Colombian Caribbean coast in an accident also attributed to bad weather.
The location, in a jungle area, is dominated by drug traffickers and also a refuge for leftist rebels. This fuels the speculation that the helicopter may have been fired on.
The defence minister said two other helicopters taking part in the mission would have detected any gunfire and did not observe any. However, he did not rule out the possibility of an attack.
Dairo Antonio Usuga David, known as Otoniel, is the alleged head of the former right-wing paramilitaries known as Clan Usuga and leads 2,000 men. The United States has offered a reward of up to $5 million for information leading to his arrest.