Sixteen Colombian police officers died when their Black Hawk helicopter crashed while taking part in a manhunt for the nation's most-wanted drug trafficker.
Two other uniformed personnel were in critical condition and being treated for serious burns after the second deadly air accident affecting the US-trained military in less than a week.
The authorities attributed the crash to bad weather. But the location, in a dense jungle near the Gulf of Uraba dominated by drug traffickers and also a refuge for leftist rebels, immediately fuelled speculation that the helicopter may have been fired on.
Colombia's biggest newspaper, El Tiempo, posted on its website an audio recording it said was a cockpit recording from an aircraft that was accompanying the crashed helicopter.
In the recording, an unidentified person remarks that the downed aircraft appeared to have been shot at from the ground and possibly was hit by a home-made mortar shell often used by rebels.
While not ruling out the possibility of an attack, defence minister Luis Carlos Villegas said two other helicopters participating in the mission would have detected any gunfire and did not observe any.
He said the most likely hypothesis was that low-lying cloud cover obstructed the pilots' visibility and the Black Hawk crashed at a speed of 110mph into a hillside. The aircraft was destroyed, he said.
Police said the Black Hawk was part of a mission hunting Dairo Otoniel Usaga, leader of Colombia's most violent drug-smuggling gang.
Since February, authorities with the support of the US Drug Enforcement Administration have intensified the manhunt for Otoniel, for whose capture the United States has offered a 5 million US dollar (£3.2 million) reward.
The incident follows the death of 11 air force personnel whose CASA-235 aeroplane crashed last week near the Caribbean coast in an accident also attributed to bad weather.
Mr Villegas lashed out at former president Alvaro Uribe, who on Twitter said he had information that the downed Black Hawk had been hit while in the air.
"Uribe knows that I don't hide information," Mr Villegas said at a news conference in Bogota.
The former president, a conservative hardliner, is a fierce opponent of the peace talks that the government has held for more than two years with the Revolutionary Armed Forces of Colombia.
Any indication that the rebels were behind either crash would probably further weaken already plunging public support for the talks.