Marxist rebels in southern Colombia ambushed an army convoy with explosives and gunfire Wednesday, killing eight soldiers and wounding four others in the second deadly guerrilla attack in as many days, the military said.

President Alvaro Uribe (search) late Wednesday blamed both attacks on errors by members of the military, and urged soldiers to exercise more caution.

In Wednesday's attack, soldiers were traveling along a highway near Santa Ana, 350 miles southwest of the capital, Bogota, when their vehicles came under attack from fighters of the Revolutionary Armed Forces of Colombia (search), or FARC (search), according to the military. One civilian was also killed.

That assault came a day after the FARC, in a struggle for control of a jungle river used for cocaine trafficking, fired rockets into a Colombian marine post, killing at least 15 soldiers and wounding 25.

It was the deadliest assault on the military since President Alvaro Uribe came to power more than two years ago on promises to destroy the FARC.

In both Tuesday's and Wednesday's attacks, Uribe said the military committed "supervision errors, control errors, vigilance errors."

Regarding the attack on the marine post, the president said some soldiers were given permission to leave their posts for some fun and relaxation, which left the remaining soldiers vulnerable. The same lieutenant who gave the soldiers permission died in the attack, Uribe said.

Faced with a massive army buildup, the FARC mostly avoids showing itself except in occasional hit-and-run attacks. Uribe's security crackdown, however, has sharply reduced homicide and kidnapping rates.

Colombia is embroiled in a 40-year-old civil war pitting the FARC and a smaller rebel group against right-wing paramilitary factions and government forces, killing an estimated 3,500 people, mainly civilians, every year.