Rodrigo Rivera steps down amid the perception that security in Colombia has deteriorated in the past year. Massacres have become almost a weekly occurrence, and kidnappings are up 9 percent.
Adm. Edgar Cely said that members of the guerrilla group are hiding in Venezuela, a claim that Colombian President Juan Manuel Santos has avoided in order to boost relations with Caracas.
The guerrilla group attacked a military contingent Tuesday, killing two civilians and wounding 10. But the Colombian government says the attack is a sign of the rebels' desperation.
Colombia troops killed top FARC rebel leader Jorge Briceño, better known as 'Mono Jojoy,' along with another 20 guerrillas of the Revolutionary Armed Forces of Colombia, in a bombing raid Wednesday.