Nine police officers were killed Wednesday when a roadside bomb planted by leftist rebels destroyed their passing truck in central Colombia, a police spokesman said.

The heavily armed police unit was supporting a counter-narcotics team eradicating coca bushes, the base ingredient of cocaine, near Landazuri, 100 miles north of Bogota, Sgt. Alberto Cantillo, a police spokesman in Bogota, told The Associated Press.

Police said the bomb was planted by the Revolutionary Armed Forces of Colombia, which is believed to operate in the rural zone.

"Where there's coca, you'll find guerrillas," said Cantillo.

Six officers were injured, Cantillo said. All were members of a mobile unit operating out of the northeastern city of Bucaramanga.

Cocaine smuggling helps finance the rebel group, Latin America's oldest and most potent rebel insurgency, now in its fifth decade.

Right-wing paramilitary groups also profit from the drug trade in Colombia, the source of 90 percent of the cocaine consumed in the United States.

Coca eradication — which is bolstered by some US$600 million in annual U.S. aid to Colombia — is a deadly activity.

Last year 26 military and police officers were killed while protecting crews manually uprooting coca bushes or applying the herbicide glyphosate from U.S.-supplied crop-duster planes.