FACTBOX: Key facts about Colombia's FARC guerrillas

(Reuters) - A French medical mission has arrived in Colombia in an attempt to treat rebel hostage Ingrid Betancourt, a French-Colombian citizen believed to be seriously ill after more than six years in guerrilla captivity.

Following are some facts about the Revolutionary Armed Forces of Colombia, or FARC, Colombia's largest rebel group and Latin America's oldest left-wing insurgency, which is holding hundreds of captives for ransom or political leverage.

* The Revolutionary Armed Forces of Colombia, known as the FARC by its Spanish initials, was established in the 1960s as a Communist-inspired peasant army fighting for land reform and to reduce the gulf still dividing rich and poor in the Andean country.

* Branded a terrorist organization by the United States and European Union, the FARC has been driven onto the defensive by President Alvaro Uribe's U.S.-backed security campaign. The United States has given Colombia $5.5 billion in mostly military aid over the last seven years.

* U.S. and Colombian authorities say the FARC has used the multibillion-dollar Colombian cocaine trade to fund its operations. Colombia's four-decade-old conflict is now often a fight over drug-producing land involving the FARC, right-wing paramilitaries and other narcotics gangs.

* The FARC still holds sway in some rural areas where it grows coca, the raw material for cocaine, and keeps kidnap victims hostage in secret jungle camps. The captives include three American defense contractors taken in 2003, and Betancourt, captured during her 2002 presidential campaign.

* Violence has eased and the economy has expanded in Colombia's central, north and northwest urban areas, but the FARC is still a potent force in the southern jungle regions where the state's presence is still weak.

* Two top rebel commanders were killed in March, a serious blow to the FARC. One, Raul Reyes, was a FARC spokesman and contact for negotiations over hostages. Reyes was killed in his camp in Ecuador in a cross-border strike that sparked a diplomatic crisis in the Andean region.

(Reporting by Patrick Markey, editing by Patricia Zengerle)