Colombia's government and rebels from the National Liberation Army have agreed to revive a stalled peace effort, providing a boost to president Juan Manuel Santos after voters rejected a deal with the much-larger Farc guerrilla group.
The rebels and government officials said formal peace talks will begin on October 27 in Ecuador.
In a brief statement from Venezuela, whose socialist government is co-sponsoring the peace process, the guerrilla group known as the ELN committed itself to freeing two captives it has been holding for months before talks begin.
Additional unspecified humanitarian actions on both sides would also take place.
In March, the ELN and the government announced they would start formal peace negotiations, but the effort never got off the ground after the government demanded the ELN renounce kidnapping and free a prominent politician who turned himself over to the rebels to secure his brother's release.
Earlier on Monday, the group handed over to the International Red Cross a rice farmer, Nelson Alarcon, it had held captive for months. He was the third person freed by the group in an area near Colombia's border with Venezuela in the past two weeks.
Mr Santos, winner of this year's Nobel Peace Prize, has staked his presidency on ending half a century of bloody combat in Colombia, but after signing a deal with the Revolutionary Armed Forces of Colombia (Farc) in front of world leaders on September 26, he saw his hopes for peace shattered by voters' rejection of the accord in a referendum six days later.
Since the defeat, he has been scrambling to build a broader coalition in support of peace, one that would include the opposition and finally bring the ideologically strident ELN to the negotiating table after more than two years of exploratory talks and false starts.
In a televised address he celebrated the apparent breakthrough and pledged not to give up on a peace deal with Farc.
"Now that we're advancing with the ELN our peace will be a fuller one," Mr Santos said
But he also sent a sharp message to opponents led by former president Alvaro Uribe, urging them not to delay consultations unnecessarily and be realistic in their proposals to adjust the 297-page accord that took more than four years to negotiate.
"We have to work with speed and promptness because our biggest enemy now is time," Mr Santos said. "The eyes of the world are upon us and they expect the best."
The ELN is Colombia's second-largest rebel group, with about 1,500 fighters, and largely finances its insurgency through extortion and kidnappings. Like Farc, it is classified by the US government as a foreign terrorist organisation.
Unlike the peasant-based Farc, the ELN shares a tradition with other leftist insurgencies in Latin America that were formed by urban students and intellectuals after the Cuban revolution.
Of the two remaining captives the ELN referred to in its statement, the most prominent is politician Odin Sanchez, who in April handed himself over to the rebels to secure the release of his brother, a former governor of Choco state who had been held by the rebels for almost three years. The ELN had been demanding a million US dollars ransom for his release.
Family members said they had been anxiously awaiting Mr Sanchez's return but were confident he would be released in the coming hours or days.
"If today they are sitting together to initiate the negotiations it's a good omen," sister Astrid Sanchez told the RCN network. "It's a sign that the ELN is going to pursue peace that we've all been longing for all these years."