Rebels killed 17 soldiers in an attack on a Colombian army patrol, officials said Friday, in one of the worst setbacks this year for the government's U.S.-backed fight for control of the country.
The late Thursday night ambush occurred in Norte de Santander province near the Venezuelan border and was carried out by rebels from the 42-year-old Revolutionary Armed Forces of Colombia, or FARC, using rifles and homemade mortars.
The army said new troops had been sent to regain control of the area. "The operation is continuing," an army spokesman told local radio.
The ambush came a month after the FARC, which uses Colombia's multibillion-dollar cocaine trade to fund its operations, killed 16 officers in an attack on a police command in the northern province of Cordoba.
Both Cordoba and Norte de Santander were home to a large number of right-wing militias formed in the 1980s to help landowners protect their property from the rebels.
Many of the paramilitary militias have disbanded as part of a peace deal with the government promising benefits including reduced jail terms. The paramilitaries, also tied to the cocaine trade, have carried out some of the worst atrocities of Colombia's guerrilla war.
"As soon as the paramilitaries left these strategic areas, the FARC moved in and are now fighting both the army and the remaining paramilitaries that did not want to disband," said Pablo Casas of the Bogota think-tank Security and Democracy.
"It is a high priority for the government to take control of these areas, not only in military terms but in terms of normal governance," he said.
The FARC offensives have dampened hope that President Alvaro Uribe can negotiate an exchange of rebels held in government jails for hostages, including three American defense contractors and former presidential candidate Ingrid Betancourt, held by the FARC in secret jungle camps.
This Andean country has received billions of dollars in U.S. aid aimed in part toward defeating the rebels and disbanding the paramilitaries, who have infiltrated Colombia's Congress and other institutions.
Three members of Uribe's Congressional coalition have been jailed for supporting the "paras," and more lawmakers are under investigation for possible links to the militias.