Two soldiers were killed and two children injured in a blast in northwestern Colombia, authorities said Monday, blaming leftist FARC rebels for the attack.
A device exploded Sunday in a rural area of the San Andres de Cuerquia municipality, "triggered remotely by a cell phone," said the town mayor Oscar Sepulveda.
The two children "aged 4 and 11 are in grave condition," he added, saying authorities were in pursuit of guerrillas from the FARC's Front 36, believed to be behind the attack.
Colombian Air Force medic Lorena Lopez told reporters the four-year-old was in the worst shape, with "injuries to his head and chest. Shrapnel severely hurt them both."
The two, cousins, were transferred by air force helicopter to a medical center in Medellin.
The incident comes as peace talks between the FARC and the government resumed Monday in Cuba, after a week's recess.
The sides have been negotiating since November to try to bring to an end Latin America's longest insurgency after nearly 50 years of guerrilla warfare.
The last attempt at a political settlement collapsed in 2002 after rebels used the talks and the creation of a demilitarized zone the size of Switzerland to regroup and rearm.
The FARC, with some 8,000 fighters, was founded in 1964 as an armed agrarian movement to fight the concentration of land ownership in huge haciendas.