Three Ecuadorian journalists who were abducted by dissident Colombian rebels have been murdered, Ecuador’s president confirmed on Friday.

Lenín Moreno offered a reward of $100,000 for information that leads to the capture of the rogue guerrilla leader known by the alias “Guacho”, who is believed to be responsible for the abduction and murder of the journalists.

Moreno said that Ecuador was “grieving” over the killed men, having previously given the captors 12 hours in which to prove that the hostages were alive before facing a military response. “We’re not going to let ourselves be intimidated,” he said.

Moreno appeared make good on his threat, immediately ordering the resumption of military operations on the border and dispatching representatives from the Catholic church in order to mediate the recovery of bodies.

“We can’t allow the criminals to impose their rules,” Moreno said in an earlier statement on Thursday night after he returned early from

Peru, where he had been due to attend this weekend’s Summit of the Americas. “We’re going to fight them in the realm they have chosen and we are going to defeat them,” Moreno went on to say.

Reporter Javier Ortega, photographer Paul Rivas and their driver Efraín Segarra, who work for Ecuadorian daily El Comercio, were kidnapped on 26 March by a holdout faction of Colombia’s Revolutionary Armed Forces of Colombia, or Farc, the leftist rebel group which laid down its weapons and became a political party after signing a 2016 peace deal.

On Thursday, Colombia’s RCN network passed on to officials graphic photos purporting to show the men’s bodies, which Ecuadorian authorities are analysing. Moreno said there is an “enormous possibility” that images are authentic.

About 1,200 former Farc rebels are believed to have joined dissident drug- trafficking factions, including the Oliver Sinisterra Front, which is believed to have kidnapped the men.

A proof of life video was released last month showing the men calling on that country’s authorities to release three unidentified combatants and end anti-narcotics cooperation with Colombia in exchange for their freedom.

The three men were kidnapped investigating heightened violence in Esmeraldas, a province on the Ecuadorian side of the 364-mile border.

The region has long been a hotbed for Colombian drug traffickers and rebel groups (which are often the same), and has been the setting for a string of recent attacks against military targets.

Moreno announced in March that he was boosting security to the region, sending 12,000 soldiers and police to combat drug gangs.

The uncertainty over the fate of the hostages has caused consternation among press freedom groups in both countries, who accuse both governments of acting too slowly.

“We condemn the actions of the Colombian and Ecuadorian governments and their lack of seriousness in protecting the reporters’ lives,” a statement from Colombia’s Foundation for Press Liberty said.

Colombia’s president, Juan Manuel Santos, has sent top military and police officers to Quito in order to assist with the crisis. “I spoke with Moreno, and I reiterated that he has and will have all of my support, and that of our armed forces and the Colombian people,” he tweeted on Thursday night.