A bomb in a backpack exploded Friday in front of a school in the Pacific port city of Buenaventura, killing one person and injuring two more, authorities said.

It was the second attack in as many days attributed to the Revolutionary Armed Forces of Colombia, or FARC, Latin America's oldest and most potent leftist insurgency.

"An explosive left by urban militias loyal to the FARC exploded when a police dog approached to smell it," vice admiral Flaminio Malaver, commander of the navy's Pacific fleet, told Caracol Radio.

A more deadly tragedy was avoided because the bomb detonated before students arrived for morning classes at the school in a poor neighborhood of Buenaventura.

Elvira Casanova, 42, was struck in the head by the blast while walking past the school and died a local hospital, Gustavo Castillo, a doctor at Buenaventura's regional hospital, told Caracol.

On Thursday, eight people were injured, two seriously, when a car bomb exploded near a radio station in the southern city of Neiva as the town's pro-government mayor was giving an interview there.

The attacks may have been in retaliation for President Alvaro Uribe's decision this week to rule out amnesty for leftist rebels under an eventual peace deal, reversing a long-standing blueprint for ending Colombia's five-decade civil conflict.

Buenaventura has suffered more than most Colombian cities from the violence. The city is home to Colombia's largest port, and leftist rebels, far-right militias and other illegal armed groups regularly battle each other for control of its lucrative cocaine trade.