MEDELLIN, Colombia (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 a campaign under way and we want to denounce it,” Venezuelan Foreign Minister Nicolas Maduro told reporters. “The government of the United States is directly responsible for this campaign, 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 and e-mails found on Reyes’ computer indicate Venezuelan President Hugo Chavez and Ecuadorean leader Rafael Correa provided financial support to the rebels.

Both deny the charges and called the Colombian military raid a U.S.-backed violation of Ecuador’s sovereignty.

“The e-mails raise serious questions about Venezuela’s relationship with the Colombian guerrillas that deserve serious answers,” said New York-based Human Rights Watch in a statement sent to reporters.

“At the very least, they appear to show that guerrilla commanders who were engaged in horrendous abuses believed they had the backing of the Venezuelan government,” it said.

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.