QUITO (Reuters) - Two Ecuadorean journalists and their driver, who were kidnapped last month by Colombian insurgents, have been killed, the leaders of both nations said on Friday, vowing justice.

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“Regrettably, we have information that confirms the murder of our compatriots,” Ecuadorean President Lenin Moreno said on state television. “It seems these criminals never planned to deliver them back safely.”

On Thursday, Moreno gave the group, former fighters from the Revolutionary Armed Forces of Colombia (FARC) who refused to demobilize under last year’s peace deal with Colombia, 12 hours to prove the hostages were alive or face a military operation.

Moreno returned to Ecuador that day from a regional summit following reports El Comercio reporter Javier Ortega, photographer Paul Rivas and driver Efrain Segarra were killed.

On Wednesday, a statement apparently issued by the Oliver Sinisterra front - a faction of the former FARC guerrillas that refused to adhere to a 2016 peace agreement - reported the Ecuadoreans had died in a failed rescue operation.

Colombia denied any rescue attempt.

The journalists and their driver were on assignment for the Quito-based El Comercio newspaper on the border between Ecuador and Colombia when they were seized on March 26.

A proof-of-life photograph released shortly after their kidnapping showed them chained and padlocked by their necks.

Colombian President Juan Manuel Santos pledged full cooperation with Ecuador and said operations had begun against the rebels on both sides of the border.

“The FARC no longer exist... These are criminals dedicated to drug-trafficking,” he said at the summit in Lima. “They will feel the full force of the law and our armed forces.”

More than a thousand FARC fighters refused to demobilize under the accord with Santos and continued trafficking across the nation. Those operating in Colombia’s southern jungles have attacked Ecuadorean security forces along the border.

The FARC, which battled for more than a half century, attacked military targets and civilian towns but generally allowed journalists to work freely, unless they went against the rebels’ interests.

The media crew was reporting on violence in the Esmeraldas region of the border when they were snatched by a group led by an Ecuadorean man identified as Walter Artizala, alias “Guacho.”

Colombia and Ecuador have both offered $100,000 each for information leading to his capture.