By Nelson Bocanegra

MEDELLIN, Colombia, June 3 (Reuters) - Venezuela on Tuesday accused the United States of trying to spread violence in the Andean region after a U.S. official said left-wing Colombian rebels were hiding in Venezuelan territory.

Colombia and the United States have long said Venezuela is not doing enough to combat Marxist FARC fighters waging Latin America's longest insurgency. The rebels are also deeply involved in drug trafficking.

Deputy U.S. Secretary of State John Negroponte on Monday urged Venezuela to crack down on rebels hiding on its side of the border.

Venezuela's left-wing government, which has voiced solidarity with the rebels' goals, called Negroponte's statement "irresponsible and abusive".

"There is an operation underway and we want to denounce it," Venezuelan Foreign Minister Nicolas Maduro told reporters. "The government of the United States is directly responsible for this operation, which is intended to fill our region with violence."

Maduro, speaking at a meeting of the Organization of American States in Medellin, Colombia, said Venezuela has not offered sanctuary to rebels who have been fighting the Colombian state for four decades.

Colombia, which has received $5.5 billion in mostly military aid from the United States over the last seven years, shares a 1,390-mile (2,237-km) border with Venezuela.

Tensions between the neighboring countries increased after a Colombian military raid into Ecuador in March which killed a top rebel commander, Raul Reyes.

Colombian and U.S. officials say files found on Reyes' computer indicate Venezuelan President Hugo Chavez and Ecuadorean leader Rafael Correa provided financial support or backing to the rebels.

Both leaders deny those charges and called the Colombian military operation a U.S.-backed violation of Ecuador's sovereignty. Chavez and Correa briefly reinforced troops on their borders with Colombia after the incursion.

Colombia is Washington's closest ally in South America while Correa and Chavez are fierce critics of U.S. policy. Colombia's war often spills over into neighboring countries. (Writing by Hugh Bronstein, editing by Alan Elsner)

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