Colombia's Defence Minister Pedro Sánchez says he is offering a record reward for information leading to the capture of a rebel leader known as "Marlon".
"Marlon", whose real name is Iván Jacob Idrobo Arredondo, is suspected of having ordered Saturday's bomb attack on the Pan-American Highway, in which 20 people were killed.
The attack is one of the deadliest targeting civilians and comes just over a month before presidential elections scheduled for 31 May.
Sánchez said the 5bn peso ($1.4m; £1m) reward for "Marlon" was the highest offered by Colombia.
The defence minister accused "Marlon" of being behind Saturday's attack as well as a series of others in the provinces of Cauca and Valle del Cauca, in south-western Colombia, over the weekend. No evidence or details have been released.
