The Colombian government and leftist FARC rebels have resumed peace negotiations in Havana.
The talks have resumed after a break of more than two weeks, during which 19 soldiers and a number of rebels were killed.
Rural protests left four farmers dead and several police injured.
More than 200,000 people have died and millions have been displaced in fighting since the FARC, or Revolutionary Armed Forces of Colombia, was founded in 1964 as a communist agrarian reform movement.
The talks, which began in November, break every few weeks, then resume, even as the longest, and last, armed conflict in Latin America rages on.
Colombian former vice president and lead government negotiator, Humberto de la Calle said: "Many Colombians do not understand why we are in a dialogue when attacks by armed groups continue."
Patience with the FARC, considered a terrorist group by the United States and the European Union, has deteriorated in recent weeks.
There has been an escalation of violence that culminated last weekend in the death of 19 soldiers and the announcement that the guerrillas had kidnapped US citizen Kevin Scott Sutay in June and now wanted to free him.
15 of the soldiers were ambushed by the FARC as they protected an oil pipeline under construction and four others were attacked in the south of the country.
Impoverished farmers in Catatumbo have blocked roads and clashed with police in the past month to protest against the government's regular fumigation of illegal coca crops.
Coca is the raw material that makes cocaine - the only means of subsistence for many Colombians.
The protesters want to be able to farm coca without government hindrance, as well as substantial increases in spending on roads, health, education and job creation.
Police said the rebels are behind the protests and have fomented the unrest, but the farmers deny that.
Santos initiated the peace talks last year in the belief that the FARC had been so weakened by the government's 10-year, US-backed offensive that its leaders were ready to end the fighting.
Three previous peace efforts have failed. The rebels have been pushed into far corners of the country, but they still have
an estimated 8,000 fighters and regularly attack oil and mining operations vital to Colombia's economic growth.