KIM HOUSEGO
Associated Press

BOGOTA, Colombia - Army troops in southern Colombia killed the commander of an elite guerrilla unit blamed for a string of high-profile attacks and kidnappings, officials said Tuesday.

Humberto Valbuena, the head of the Teofilo Forero unit of the Revolutionary Armed Forces of Colombia, or FARC, was killed Monday along with three other rebels during an offensive in remote jungles in Caqueta state, an army spokeswoman said.

Valbuena, alias "Grass," was one of the rebels who "carried out the largest number of kidnappings and extortion in the country," Gen. Carlos Alberto Fracica, the commander of the "Plan Patriota" offensive, told reporters.

Valbuena's killing came less than a year after he took over command of the Teofilo Forero unit from his slain predecessor, Edgar Gustavo Navarro, also known as "the Maimed," because he lost his right thumb in combat.

Authorities blame the Teofilo Forero for the abduction of three American defense contractors after their anti-drug plane crashed in a guerrilla stronghold in February 2002, as well as several deadly bombings in the capital, Bogota.

Separately, the United Nations said Tuesday it was increasingly concerned over the fate of Afro-Colombian and indigenous communities in northwest Colombia amid reports that FARC fighters and their outlawed right-wing paramilitary foes were massing in the area.

"Blockades imposed by the armed groups to prevent goods from reaching their enemies have also increased, tightening their stranglehold on the population," U.N. spokesman Ron Redmond told reporters in Geneva. "Civilians are suffering from a marked increase in malaria and malnutrition."

Rebels and the paramilitaries have long battled for control of the area in northwestern Choco state, which is a strategic corridor for arms and drugs trafficking through nearby Panama.

In May 2002, 119 villagers huddling in the Bojaya church were killed when the building was destroyed by a guerrilla mortar round - one of the worst tragedies of Colombia's 40-year-old civil war.

The conflict, which claims the lives of 3,500 people every year, pits the FARC and a smaller rebel group against paramilitary fighters and government forces.