SANTO DOMINGO — President Uribe of Colombia said today that Colombian rebels helped President Correa of Ecuador get elected, citing as evidence a rebel’s letter seized during a cross-border raid that has sparked an international crisis.

Mr. Correa walked out of the 20-nation Rio Group summit after the accusation, then returned and demanded the opportunity denounce the accusation as “infamy.”

Mr. Uribe said his forces seized a letter during their raid Saturday on a rebel camp just across the border with Ecuador in which Raul Reyes — a rebel leader killed in the raid — told the guerrillas’ top commander about “aid delivered to Rafael Correa, as instructed.”

Mr. Uribe also said that he didn’t give Mr. Correa advance warning of the attack on Ecuadorean soil because “we haven’t had the cooperation of the government of President Correa in the fight against terrorism.”

That prompted an angry exchange between the two, as other presidents sought to keep the dialogue civil.

Mr. Correa, who has broken off relations with Colombia and sent troops to the border over the incident, denounced Mr. Uribe as a liar, portrayed Ecuador as a victim of Colombia’s conflict, and proposed an international peacekeeping force to guard their border.

“I reject this infamy that the government of Rafael Correa has collaborated with the FARC,” Mr. Correa bellowed into the microphone. His comments drew loud applause from other leaders, who met Mr. Uribe’s speech with silence.

The summit was to have focused on energy and other issues, but those were overshadowed by the diplomatic crisis in the Andes after the deadly Colombian cross-border raid into Ecuador on Saturday that killed a senior Colombian rebel and 24 others.

It began quietly, with the host, President Fernandez of the Dominican Republic, appealing for unity. President Chavez of Venezuela said it was time to cool tensions and predicted the summit “is going to be positive.”

“People should go cool off a bit, chill out their nerves,” Mr. Chavez said before the summit started. “I think the meeting today is going to be positive, because it is going to help the debate. We have to debate, talk, and this is the first step toward finding the road.”

But the accusations began quickly, with Mr. Correa criticizing “the aggression of Colombia” and Mr. Uribe saying that Mr. Correa is a dishonest partner in the fight against the Revolutionary Armed Forces of Colombia, or FARC.