The Colombian government said on Wednesday it will hold formal peace talks with the second largest rebel group, the National Liberation Army (ELN), amid efforts to end the country's five-decade conflict.
The talks will open a new front in peace negotiations as the government also closes in on a deal in Cuba's capital, Havana, with Colombia's biggest guerrilla group, the Revolutionary Armed Forces of Colombia (FARC).
Starting as a peasant uprising in the 1960s, and drawing in various armed groups and gangs, the conflict has killed more than 260,000 people, uprooted 6.6 million people, and left a further 45,000 missing.
"If we can make peace, it will be the end of guerrilla fighters in Colombia," said Colombia President Juan Manuel Santos.
Government and ELN officials announced the peace negotiations at a press conference in the Venezuelan capital of Caracas - the two sides have held exploratory talks in Ecuador for more than a year.
The talks will kick off in Ecuador and then continue in Venezuela, Brazil and Chile and Cuba. The five countries, along with Norway, will act as guarantors of the negotiations.
Inspired by Cuba's 1959 revolution and established by radical Catholic priests in 1964, the ELN has battled a dozen Colombian governments since it was founded.
Al Jazeera's Alessandro Rampietti, reporting from Colombia's capital, Bogota, said the start of peace negotiations with the ELN was a "very important" step in the effort to end half a century of fighting.
"The presence of the ELN in the talks here makes [the prospect of peace] much more real and makes people here more hopeful about being able to ending this very long conflict," Rampietti said.
He added that ELN's absence until now from the negotiating table "was seen as the elephant in the room" in efforts to end the conflict, with many in the government fearing a potential breakthrough in Havana risked allowing the ELN to make inroads into areas under the influence of FARC.
"Actually, in the last couple of weeks we have heard rumours of supposed ELN fighters operating, or at least moving about, in territory that is under control of the FARC," Rampietti said.
Colombia's Santos has staked his presidency on ending the conflict with the guerrilla groups.
The government has been holding separate talks with the FARC in Havana for more than three years. The two sides say they have made substantial progress over recent months, but last week failed to reach a self-imposed deadline for a final accord.
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Yet, as the talks with the FARC have advanced, tensions have remained high over the ELN, which has continued committing attacks and abductions.
Unlike the FARC did last year, the 2,000-strong ELN has not yet ordered a ceasefire by its troops, who live in hiding. Yet the group recently freed two hostages, which Santos had placed as a condition ahead of the start of formal talks.
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Source: Al Jazeera and agencies