BOGOTA -- Five soldiers were killed and two others wounded by FARC guerrillas in the jungle around Calamar, a town in southern Colombia, the army said Sunday.

The soldiers were ambushed Saturday afternoon while providing security for peasants hired to manually eradicate coca fields in La Paz, a village east of Calamar, which is in Guaviare province.

The soldiers, who belonged to the army's 4th Division, were protecting the peasants from the 1st Front of the Revolutionary Armed Forces of Colombia, or FARC, military spokesmen at the unit's headquarters in the central city of Villavicencio said.

The FARC unit had been preventing residents from eradicating the illegal crops under a voluntary program, the army said.

"The terrorists, utilizing (gas) cylinders packed with explosives in an indiscriminate manner, murdered the soldiers who were supporting the eradication work," the army said.

A sergeant and a corporal were wounded in the attack, the army said, adding that the two men were taken to Bogota, where "they are recovering."

A FARC guerrilla who allegedly carried out more than two dozen bombings across Colombia was arrested early Saturday in Bogota, police said.

Edilberto Cruz Rubio was detained in Bosa, a district in the southern section of the capital, Dijin judicial police agency chief Col. Luis Gilberto Ramirez said.

Cruz was trained in explosives and was known to be an expert in bomb making among the guerrillas, Ramirez said.

The guerrilla faces rebellion, terrorism and murder charges in connection with 27 bombings, Ramirez said.

Cruz, who belonged to the FARC's 27th Front, was in Bogota on a mission, Ramirez said.

The FARC, Colombia's oldest and largest leftist guerrilla group, was founded in 1964, has an estimated 8,000 to 17,000 fighters and operates across a large swath of this Andean nation.

President Alvaro Uribe's administration has made fighting the FARC a top priority and has obtained billions in U.S. aid for counterinsurgency operations.

The FARC, whose leader is Alfonso Cano, suffered a series of blows last year.

On July 2, 2008, the Colombian army rescued former presidential candidate Ingrid Betancourt, U.S. military contractors Thomas Howes, Keith Stansell and Marc Gonsalves, and 11 other Colombian police officers and soldiers.

The FARC had been trying to trade the 15 captives, along with 25 other "exchangeables," for hundreds of jailed guerrillas.

The rebels' most valuable bargaining chip was Betancourt, a dual Colombian-French citizen the FARC seized in February 2002 whose plight became a cause celebre in Europe.

The guerrilla group is believed to still be holding some 700 hostages.

FARC founder Manuel Marulanda, who was known as "Sureshot," died on March 26, 2008.

Three weeks earlier, Colombian forces staged a cross-border raid into Ecuador, killing FARC second-in-command Raul Reyes and setting off a regional diplomatic crisis.

Ivan Rios, a high-level FARC commander, was killed that same month by one of his own men, who cut off the guerrilla leader's hand and presented it to army troops, along with identification documents, as proof that the rebel chief was dead.

A succession of governments have battled Colombia's leftist insurgent groups since the mid-1960s.

The origin of Colombia's civil strife dates back to 1948, when the assassination of popular politician Jorge Eliecer Gaitan sparked a 10-year-long civil war known as "La Violencia."

About six years after that conflict ended with a power-sharing pact between Colombia's two main parties, a government offensive against peasant self-defense groups led Marulanda, who was pursued by death squads during La Violencia, to form the FARC.

In 1999, then-President Andres Pastrana allowed the creation of a Switzerland-sized "neutral" zone in the jungles of southern Colombia for peace talks with the FARC.

After several years of fitful and ultimately fruitless negotiations, Pastrana ordered the armed forces to retake the region in early 2002. But while the arrangement lasted, the FARC enjoyed free rein within the zone.

The FARC is on both the U.S. and EU lists of terrorist groups. Drug trafficking, extortion and kidnapping-for-ransom are the FARC's main means of financing its operations.