(Refiling with UPDATE 1 in headline) (Adds U.S. comment on Venezuela, quotes)

By Nelson Bocanegra

MEDELLIN, Colombia, June 2 (Reuters) - The Organization of American States said on Monday it will probe claims by Colombia that Ecuador has cooperated with leftist guerrillas and the United States called on Venezuela to get tough on the rebels.

Diplomatic tensions have risen between Colombia and its two neighbors since a Colombian military raid on Ecuador's side of the border in March killed Raul Reyes, a top guerrilla leader.

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.

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), which is fighting a four-decade-old insurgency.

"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.

Deputy U.S. Secretary of State John Negroponte, also speaking in Medellin, suggested Venezuela could do more to fight the FARC, which is labeled a terrorist group by Washington.

"As far as the government of Venezuela is concerned, I don't think there is any doubt that there are FARC who have sought sanctuary on Venezuelan soil," Negroponte told reporters.

"I would suggest that those who are in a position to do something about that need to think about the long-term bilateral relationship between the two countries and whether it is really in the interest of their country to allow that type of situation to continue," Negroponte added.

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

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