Marxist rebels in Colombia have resumed attacks on oil installations just as a fresh round of peace talks were set to start in neighbouring Ecuador.
Members of National Liberation Army or ELN carried out three bombings on a Colombian oil pipeline plus a grenade attack on a naval base.
Colombian President Juan Manel Santos has recalled his chief negotiator.
"I have told the head of the government's delegation in Quito to return immediately to evaluate the future of the peace process, and reiterated this morning to our armed forces the order to act forcefully."
Last September the ELN agreed on a temporary ceasefire with the Colombian government but that expired on Tuesday. It's not clear why the group resumed attacks despite a government offer to extend the truce.
During the ceasefire, reached on Sept 4, the insurgent group promised to suspend hostage-taking, attacks on roads and oil installations, the use of landmines and the recruitment of minors. In turn, the government agreed to improve protection for community leaders and conditions for about 450 jailed rebels.
The 2,000-strong ELN has hurt the oil industry with its regular bombings of infrastructure and has taken numerous oil workers hostage over the years.
The breakdown in the peace process has raised concern at the UN.
"The next few months must be the opportunity to turn the corner as it were, and establish what is still a fragile process on a more durable basis," said Special Representative Jean Arnault for UN Mission in Colombia.
Colombia hopes to sign a peace deal like that achived with the larger larger Revolutionary Armed Forces of Colombia or FARC in 2016.
But the diffuse command structure of the ELN makes it harder to negotiate.
The ELN, founded by radical Roman Catholic priests in 1964, has sought peace with the government before but made little progress. It is considered a terrorist group by the United States and European Union.