The contractors were flying in a Dash 8 airplane

Four passengers have died after a US anti-drug plane crashed while monitoring one of Colombia's main drug trafficking corridors in a region dominated by the FARC guerrillas and narco-paramilitaries the Urabeños.

The small plane crashed in the jungle early on October 5, killing three US contractors and a Panamanian National Guardsman, and leaving two other US contractors in critical condition, reported the Associated Press. According to US officials, the plane left Panama on a surveillance mission and was tracking a suspected smuggling vessel in the western Caribbean when it crashed near the town of Capurgana, two miles from the Panamanian border. 

The cause of the crash is as yet unknown, but officials have ruled out the possibility of the plane being shot down, according to AP. Instead they have suggested it was due to a mechanical or human error, reported EFE.

The flight was part of the US-led Operacion Martillo (Operation Hammer), a regional counternarcotics initiative targeting trafficking in Central America, through which an estimated 80 percent of US-bound cocaine travels.

InSight Crime Analysis

Capurgana is situated in the remote jungles of the Darien Gap on the border between Colombia and Panama -- one of the main dispatch points for Colombian cocaine headed to the United States through Central America. The treacherous terrain makes it difficult for authorities to maintain a consistent presence in the region, which is also the site of drug production and human smuggling.

The region has long been a safe haven for guerrillas from the Revolutionary Armed Forces of Colombia (FARC) and is near to the birthplace of Colombia's leading criminal organization the Urabeños, which also retain criminal interests in the area.

SEE ALSO: The FARC, Peace and Possible Criminalization

The FARC's 57th Front operates on both sides of the border, and has become one of the wealthiest FARC units through its involvement in drug trafficking. The 57th Front has a longstanding alliance with the Urabeños, which involves cooperating to move drug consignments and possibly even pooling together cocaine shipments. Both groups customarily arrange transportation through cocaine “brokers,” who often operate without affiliation to any one organization, making it difficult to assess whose consignment the agents were tracking when they crashed.