The Colombian army says it has killed a top commander from the country's second largest guerrilla group, the National Liberation Army (ELN).
Jose Amin Hernandez Manrique, known as Marquitos, was killed in the north-western province of Antioquia, the army said.
He led 13 ELN units in Antioquia and Bolivar provinces, according to the military.
The region is known for drugs and arms trafficking and illegal mining.
Colombian President Juan Manuel Santos, said on Twitter: "Alias Marquitos, commander of the Dario Martinez front and member of the national leadership of the ELN, has been killed. Congratulations to the armed forces."
The authorities believe Marquitos, also known as Marcos, was responsible for the 1999 hijacking of an aircraft with 46 passengers on board.
The ELN was founded in 1964 to fight Colombia's unequal distribution of land and wealth. It is now estimated to have about 2,000 active fighters.
The ELN has had exploratory talks but has not entered into peace negotiations with the government, unlike the country's largest left-wing rebel group, the Revolutionary Armed Forces of Colombia (Farc).
In April, the ELN's commander in chief, Nicolas Rodríguez Bautista, told Reuters news agency that the agreement to start formal peace talks was 80% completed.
It is unclear whether Marquitos's death will affect preliminary talks, although many Colombians feel they have stalled, says the the BBC's Colombia correspondent Natalio Cosoy.
The Farc has called several times for the ELN to join their peace talks in the Cuban capital Havana.