BOGOTA, Colombia (AP) — Three Colombian judicial investigators were killed Wednesday when their vehicle was ambushed along the country's southern border with Ecuador by a dissident rebel group, authorities said.

Officials said two of the men were incinerated to death when their car was torched by holdout guerrillas from the demobilized Revolutionary Armed Forces of Colombia.

The same group has been behind a wave of drug-related violence, including the March kidnapping of three Ecuadorean newspaper workers who were later found slain. It is led by a former FARC mid-level commander, Walter Arizala, better known by his alias Guacho, who is the target of an intense military manhunt backed by the U.S.

It's not clear what the judicial workers were investigating. The three worked for the chief prosecutor's office in Colombia's volatile Narino state, which is home to Colombia's largest harvest of illegal coca crops. Land dedicated to production of the raw ingredient used to make cocaine skyrocketed last year to 209,000 hectares — the largest amount on record, according to a recent White House report.

Officials identified one of those killed as Willington Montenegro, a 24-year veteran of the chief prosecutor's office and a lawyer by training who had been working as an explosives expert. He was accompanied by another explosives expert and a financial administrator in the organized crime unit.

Chief Prosecutor Nestor Martinez said he will honor their memory by redoubling efforts to attack criminal groups in the volatile area.

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