Three members of Colombia's Revolutionary Alternative Forces of the Commons (FARC), the former guerrilla group turned political party, were captured, tortured and shot dead by suspected rebels of the ELN in the southwest, FARC said on Thursday.
Three ex-combatants and one of their relatives were killed on Wednesday in a rural area La Florida, in Nariño province, Reuters reports.
The jungle and mountain region bordering Ecuador is rife with armed groups including as the ELN (National Liberation Army), which is now Colombia's largest remaining insurgent group after the demobilization of the FARC.
The FARC, which kept its acronym by changing its name to the Revolutionary Alternative Forces of the Commons, signed a peace accord in late 2016, putting an end to its part in a conflict which has killed more than 220,000 people over five decades.
"Everything indicates that those responsible for the crime are active members of the National Liberation Army that operates in that region of the country," the FARC said in a statement. "We urgently request the ELN publicly clarifies the information."
Under the peace accord, more than 11,000 combatants turned in their weapons and formed a political party that will present 74 candidates for legislative elections in March, as well as its former leader, Rodrigo Londono, as presidential candidate in May.
Similar peace talks with the ELN were suspended on Monday by President Juan Manuel Santos after the insurgent group launched a series of bomb attacks against police targets, killing seven and injuring dozens.
The 2,000-strong ELN and the government had been in peace talks for a year, and the two sides agreed to their first-ever ceasefire in October, but the rebels launched a new offensive when the ceasefire expired last month, killing members of the armed forces, bombing major oil pipelines and kidnapping an oil contractor.
The ELN, founded by radical Roman Catholic priests in 1964, has sought peace with the government before but made little progress. It is considered a terrorist group by the United States and European Union.
FARC leaders have expressed fear of a systematic campaign to assassinate militants and leaders of their political party, as happened with the Patriotic Union, a leftist organization that lost some 5,000 of its members in attacks attributed to right-wing paramilitaries in 1985.
According to the FARC, 39 ex-combatants have been assassinated since the peace agreement was signed, in addition to 14 family members.