The attack, one of the most serious in recent months, took place in a rural area of El Carmen municipality in Colombia's Norte de Santander province, an important region for growing coca and producing cocaine.
The government of Colombia's President Gustavo Petro restarted peace talks with the ELN last year as part of a drive for total peace in the Andean country, where almost six decades of internal conflict have left at least 450,000 dead.
Petro has called a meeting with the government's peace delegation as well as guarantor countries - which include Venezuela, Mexico and Chile, among others - he said on Twitter.
"A peace process should be earnest and accountable to Colombian society," Petro said in the message.
The government and the ELN concluded a first round of peace talks in Venezuela's capital Caracas at the end of 2022.Â
A second round of peace talks began in Mexico this year.
The ELN did not immediately comment on the attack or Petro's decision to talk with Colombia's peace delegation and guarantor countries.
High-ranking government figures denounced the attack.
"There's always the option of stepping away from the table when there aren't conditions for dialogue or... ordering a total offensive when there's no real will for peace," Interior Minister Alfonso Prada said on Twitter.
The ELN is Colombia's oldest remaining rebel group, founded by radical Catholic priests in 1964, and the talks are the cornerstone of efforts by Petro - himself a former member of another insurgent group - to bring "total peace" to Colombia.
Negotiations with the ELN under previous administrations faltered on the group's diffuse chain of command and dissent within its ranks although Pablo Beltran, the head of the ELN delegation, and top commander Antonio Garcia have said fighters are on board with these talks.
