Initial reports by several military officials indicated the soldiers were protecting government workers during a coca eradication effort when the Revolutionary Armed Forces of Colombia, or FARC, surprised them Tuesday morning.
But in a press conference Tuesday night in Bogota, Defense Minister Camilo Ospina said the workers eradicating coca, the source of cocaine, completed their task nine days ago and left the region. The troops, however, remained in the area to provide security to civilians who were being threatened by the FARC, which controls cocaine production in the area, he said.
The fighting took place just outside the Sierra Macarena National Park, a pristine reserve where the country's central grasslands meet the Amazon jungle, he said.
The main town in the remote area is Granada, 81 miles south of Bogota.
Some 400 FARC rebels took part in the attack, outgunning about 80 troops with the army's 12th Mobile Brigade, brigade commander Col. Carlos Ramirez said.
At least five other soldiers were injured, three seriously, the Colombian Army said. One more soldier remains unaccounted for and may have been kidnapped, said the minister.
An AP photographer in Vista Hermosa saw at least four injured government troops being loaded on to helicopters to be taken to nearby hospitals.
The Defense Ministry, in a statement, said an operation had been launched to pursue the attackers.
Since the beginning of the year, more than 600 government forces, including military and police, have been killed by the FARC or other illegal, armed groups, according to government statistics.
In June, several hundred FARC fighters launched an assault against a small military base in southern Putumayo, killing 22 soldiers. And in February, the FARC used homemade rockets to attack a marine outpost on the Iscuande River in southwest Colombia, killing 16 marines.
The FARC, which funds itself mainly through drug trafficking and kidnapping, is considered a terrorist organization by the United States and the European Union. Colombia is the world's leading producer of cocaine, and supplies up to 90 percent of the U.S. market.
Founded 40 years ago, the FARC, with at least 12,000 heavily armed fighters, is the country's main rebel group. Its aim is to fight for social revolution and redistribute wealth in this country of 44 million people.
Hard-line President Alvaro Uribe, backed by billions of dollars in U.S. aid to fight drug trafficking and rebels, launched a military offensive against the FARC in the southern region where Tuesday's attack occurred.
Despite the offensive, the FARC continues to have a strong presence in the region.
The government has warned that the FARC is planning a string of attacks on government troops and possibly civilians leading up to elections set for next year.
Uribe, who has not been able to convince the FARC to sit down for peace talks, is up for re-election in the May presidential vote.
Meanwhile, in La Paz, Bolivia, President-elect Evo Morales will reject U.S. economic and military aid if the United States requires continued coca-eradication efforts to get the money, a close aide to the former coca growers' leader said Tuesday.
Morales also plans to withdraw Bolivia's military from anti-drug efforts and leave the job to police, said Juan Ramon Quintana, a member of the Morales' transition team.
Morales, who won Bolivia's presidency Dec. 18 with a decisive 54 percent of the vote, campaigned on promises to stand up to the U.S. on the coca issue and the eradication of coca plantations. Coca eradication is a condition for aid from the United States, which gave Bolivia $91 million in 2005.
The decision was made "mainly for reasons of sovereignty," said Quintana, who described Bolivia's Special Force to Fight Drug Trafficking as "an appendix" of the U.S. Drug Enforcement Administration.
Bolivia's national police commander, Gen. David Aramayo, acknowledged that the United States offers "important support" in the coca-eradication campaign, but insisted that his force has been ultimately responsible for the drug unit.
In addition to being an ingredient for cocaine, coca has legal religious and medical uses. Indians also chew it to fight fatigue.
Morales once wrote on his Web site, "Thanks to coca, we've made it through the endless suffering caused by the white man's infamous war on drugs." But he's also made a point of saying he'll crack down on cocaine trafficking while protecting the plant's traditional uses.