Under intense security, Colombian police planes and helicopters have resumed U.S.-backed fumigation flights to kill drug crops growing in a former rebel stronghold.
Helicopter gunships escorted the crop dusting planes on Sunday that sprayed fields of heroin poppies.
Flights were suspended during peace negotiations. But government talks with the Revolutionary Armed Forces of Colombia collapsed late last month. Officials say drug crops flourished while the rebels occupied the Switzerland-sized area.
Colombia chief of counter-narcotics efforts, General Gustavo Socha, says officials discovered 350 hectares of heroine poppies and 15,000 hectares coca plants which provide the raw ingredient of cocaine.
President Andres Pastrana ordered the rebels to abandon their southern Colombia stronghold after the peace talks collapsed. Critics say the guerrillas used the enclave for growing and trading drugs, and holding kidnap victims for ransom.
Rebels are being blamed for the brutal killing of Senator Martha Catalina Daniels and two others trying to negotiate the release of rebel-held hostages. The three were shot in the head and their bodies dragged to a spot near Bogota where they were found Sunday.
Since the collapse of the peace talks, the 17,000 strong rebel group intensified attacks against the country's infrastructure, including water sources, power and telephone lines.
The United States provides more than $1 billion to Colombia for counter-narcotics efforts. The Colombia government has requested that Washington also allow the money to be used to fight the rebels.