Officials said the FARC rebel group staged three attacks in the southwestern state of Cauca, which is a strategic area for the production and transport of cocaine, wounding at least 77 people in addition to killing three.

Colombia, Latin America's No. 4 oil producer, has battled leftist insurgents for almost five decades, and while violence has dropped off sharply since a 2002 U.S.-backed crackdown, armed groups still carry out attacks frequently.

Guillermo Alberto Gonzalez, governor of Cauca province, said guerrillas attacked a police post with a bus loaded with explosives in the Toribio municipality, killing one police officer and two civilians and wounding 60 others.

Almost simultaneously, another band of rebels detonated a car bomb in Corinto municipality, wounding at least 11 people while another explosive attack in Siberia village injured six more, Gonzalez said.

"These attacks and the way they were carried out clearly show the cruelty and despair of the FARC," President Juan Manuel Santos said in a statement.

In mid-June, another, smaller rebel group set off a car bomb in Cauca's capital, wounding 17 people.

The FARC, Latin America's oldest insurgency, has stepped up violence recently in the world's No. 1 cocaine producer - mainly staging attacks in regions known as key cocaine-producing and transit areas.