MEDELLIN, Colombia, June 2 (Reuters) - The Organization of American States said on Monday it will investigate claims by Colombia that computer files left by a slain guerrilla chief show that neighboring Ecuador had cooperated with the rebels.

Ecuador Foreign Minister Maria Isabel Salvador requested the OAS probe as a way to prove that her country does not have links with the Revolutionary Armed Forces of Colombia (FARC).

"We have to look into the contents (of the files). The minister is asking that we clarify precisely what is real and what is not," OAS chief Jose Miguel Insulza told reporters on the sidelines of an OAS meeting in Medellin, Colombia.

Regional diplomatic tensions have increased since a Colombian military raid on Ecuador's side of the border in March killed Raul Reyes, a top left-wing rebel commander.

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.

Colombia is Washington's closest ally in the region while Correa and Chavez are fierce critics of U.S. policy. Colombia's cocaine-fueled guerrilla war often spills over into the neighboring countries. (Reporting by Nelson Bocanegra; Writing by Hugh Bronstein)

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