(Adds details on deaths, police comment) BOGOTA, May 9 (Reuters) - Left-wing rebels blew up a Colombian police truck on Wednesday, killing nine officers in one of the worst guerrilla attacks on security forces this year, authorities said. The attack was in Santander province, where officials said the second-largest guerrilla group, the National Liberation Army, or ELN, is active. But police blamed the largest rebel group, the Revolutionary Armed Forces of Colombia, or FARC. Local police commander Gen. Jaime Otero said the officers were providing security for workers eradicating coca crops, which are used to make cocaine, when FARC members detonated explosives as their truck passed by. Colombia remains the world's top producer of cocaine despite receiving more than $4 billion in U.S. military and counter-narcotics aid since 2000 -- the largest amount outside the Middle East. Violence from Colombia's 40-year insurgency has decreased since President Alvaro Uribe led a U.S.-backed security drive to retake parts of the country. But the FARC and ELN are still fighting and officials say both are now engaged in the cocaine trade.
