Three Colombian soldiers were killed Friday when their patrol set off land mines laid by leftist FARC rebels in a mountainous area of the southwestern province of Cauca, a provincial official told Efe.

"We have been informed of the death of three soldiers, of several more wounded and one missing in a mine field," provincial government Secretary Alvaro Grijalva said by telephone from Popayan, Cauca's capital.

The mines were planted by the Revolutionary Armed Forces of Colombia, or FARC, in contravention of international humanitarian law, he said.

Several squadrons from the army's 29th Brigade were in the area and the mine detonations came several hours after the Colombian air force bombed a nearby FARC camp, possibly killing a commander, Grijalva said.

"With terrorist actions and attacks," he said, the FARC is trying to sabotage Sunday's nationwide regional and local elections.

Forty-one candidates have been killed since campaigning began in February, Colombia's independent Electoral Observation Mission, or MOE, said earlier this week.

That figure represents a 52 percent increase over the last round of local and provincial balloting in 2007, the MOE said in a report to election officials.

More than 330,000 police and military personnel have been deployed to provide security for the balloting.

Around 32 million Colombians are eligible to choose among roughly 100,000 candidates vying for 13,555 offices, including provincial governorships, mayoralties and seats in regional legislatures.

Violence, whether from leftist rebels, right-wing militias or criminal gangs, is not the only obstacle to a successful process.

The MOE estimates that some 600,000 people have registered to vote in precincts where they do not reside, according to the group's director, Alejandra Barrios, who said the polling places receiving an influx of outside voters tend to be in areas with a history of vote-buying by business interests or traditional political clans.