Crude oil poured into Colombia's river water system after the attack on the 220,000-barrel-per-day Cano Limon-Covenas oil pipeline. The spill was causing widespread damage to the ecology and the resulting pollution will likely cause major shortages of fish and disrupt river transport, environmental analysts said.
It was the second most serious attack on government and state installations in recent weeks and appeared aimed at hitting the economy of Colombia, Latin America's fourth largest oil producer.
Earlier this month, a guerrilla group attacked an oil installation in Puerto Asis, southern Colombia, killing five people and injuring three others, military officials said.
The Ecopetrol oil well in was attacked with explosives and small arms fire.
"It was a demented attack against the civilian population," the Colombian army said in a statement.
It said units of the 25th Infantry Battalion were sent with the objective of launching offensive operations "against those responsible for this criminal action."
Guerrillas with the Revolutionary Armed Force of Colombia, know by the Spanish initials FARC, have attacked cities like Puerto Asis along the Ecuadorean border, which Colombian authorities said is a strategic area.
The guerrillas can launch attacks in Colombia then cross the border into Ecuador to avoid pursuit by the army, Colombia Reports said.
The 480-mile Cano Limon-Covenas pipeline is already working at about one-third of its capacity after earlier disruptions.
About 70 guerrilla attacks have targeted Colombia's oil pipelines this year, most of them seen by officials as the work of FARC.
Earlier attacks targeted a pipeline network connecting a major pipeline to an oil field in the Putumayo province, in the southwest of the country bordering Ecuador and Peru.
The pipeline is operated by the state-run Ecopetrol, formerly the Empresa Colombiana de Petroleos S.A.
Although Colombian officials and security analysts say FARC has weakened in recent years it remains a major threat to the government's program of boosting the country's oil and gas production.
Officials earlier said the government would continue to pursue its goal of producing at least 1 million barrels a day of oil. Earlier attacks in May and June affected production and kept it below 940,000 barrels a day.
The FARC challenge to the government of President Juan Manuel Santos is twofold because the guerrillas are often seen to be working with drug overlords.
Last week, the alleged No. 2 in a Colombian drug-trafficking organization was arrested in Honduras.
The operation that led to the arrest of Alexander Montoya Usuga, nicknamed "El Flaco," was run jointly by Colombia and Honduras. Montoya, 33, was allegedly traveling in an airplane stolen from El Dorado Airport in Bogota some months ago and had just flown into Honduras from a third country.
Montoya faces charges of murder and drug trafficking, authorities said.