Colombian President Juan Manuel Santos has said he was ready to start negotiating peace with the country's second-largest rebel group, the National Liberation Army (ELN), "as soon as possible".
The announcement comes a day after the ELN released a Canadian hostage it had been holding for months, Gernot Wober.
Santos hailed the rebels' release and said "the government is ready to start a dialogue with the ELN as soon as possible," in a statement released by his office on Thursday.
Santos had conditioned any peace talks with the ELN on freeing Wober and all other captives it holds in the nation's jungles.
ELN leaders have expressed interest in starting peace negotiations similar to those currently under way with the Revolutionary Armed Forces of Colombia, or FARC.
It is not known how many hostages the group holds.
'Support for peace'
"We hope that this effort contributes to a healthy exchange and support for peace in Colombia," ELN leader Nicolas Rodriguez said in a video posted on the group's website.
He said the release on Tuesday was a humanitarian gesture.
The ELN is against mining by foreign companies in Colombia.
Both the ELN and FARC have stepped up attacks on the infrastructure this year, hitting oil pipelines and power lines repeatedly.
The ELN has battled a dozen governments since it was founded in 1964 and is considered a "terrorist group" by the United States and the European Union.
It has sought peace before, holding talks with the Colombian government in Cuba and Venezuela between 2002 and 2007.
Experts say there was a lack of will on both sides to agree a final peace plan.
Meanwhile, a Colombian high court has declared constitutional a law the government says is key to its peace process with rebels but which rights activists say could lead to impunity for war crimes.
The Constitutional Court's president announced the 7-to-2 decision on Wednesday evening and said the law does not mean war crimes will go unpunished.
Congress passed the amendment last year at Santos' urging before peace talks were announced the Colombia's largest rebel group.
It establishes that rebels can receive reduced or suspended prison sentences if they lay down their arms.
Human rights groups complain the amendment could allow combatants who violate international humanitarian law to escape justice.