A regional summit of Latin American leaders has opened with a flurry of accusations over Colombia's cross-border raid into Ecuador.
Regional tensions have risen in the lead-up to the summit
Ecuador's Rafael Correa condemned Colombia's "aggression" in his opening speech in the Dominican Republic.
His Colombian counterpart, President Alvaro Uribe, responded with claims Mr Correa had links to Farc rebels and had not co-operated in fighting terrorism.
Venezuela's Hugo Chavez had called for a cooling of tensions over the raid.
The operation left some 20 rebels dead, including a senior Farc commander, Raul Reyes, but has had massive political repercussions in Latin America.
Venezuela and Ecuador, which cut diplomatic ties and sent troops to their borders after the incursion, have demanded a strong apology from Colombia.
As arguments continued at the summit, the Colombian defence ministry said another senior Farc rebel, Ivan Rios, had been killed by his own men - this time in the western Colombia province of Caldas.
Rios was the youngest man on Farc's seven-member secretariat.
Mr Uribe told Latin American leaders gathered at the Rio Group summit in Santo Domingo that if he had alerted Ecuador about the raid that killed Reyes, it would have failed.
He said Ecuador's president had not co-operated in the fight against terrorism, adding that the operation was "against one of the most tenacious terrorists in the history of humanity".
He quoted a letter allegedly seized in the raid as evidence Mr Correa had links to the Colombian rebels.
Mr Uribe said Reyes had written to Farc leader Manuel Marulanda saying: "We wait for the visit of the Ecuadoran security minister and he has greetings from President Correa to commander Marulanda."
Ecuador has moved soldiers towards its border with Colombia
Mr Correa rejected the accusations, calling them lies.
"These hands are not tainted with blood," he said.
Mr Correa admitted there had been communications with Farc, but because his government was trying to secure the release of hostages held by the rebels, including former Colombian presidential candidate Ingrid Betancourt.
He said Ecuador was paying a high price for Colombia's civil conflict spilling over onto its territory. He added that it was the fault of Colombia, not Ecuador that rebels had crossed the border.
The summit's host, Dominican President Leonel Fernandez, had earlier said he hoped the summit would be a chance to "consolidate relations".
He had been trying to find consensus on the wording of a declaration on the dispute.
Correspondents say key countries like Brazil and Chile will also be working to find a diplomatic solution to the crisis.
Before the start of the summit, Mr Chavez said he hoped the summit would be positive.
"People should go cool off a bit, chill out their nerves," he told journalists at his hotel before leaving for the summit, AP news agency reports.
"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."
Mr Correa, who has been touring Latin American capitals to rally opposition to Colombia, said Colombia had to promise not to violate its neighbour's territory and end its allegations that Ecuador supported the guerrillas.
"Of course we can put an end to... the conflict in this meeting... It's as easy as hearing unconditional apologies from President Alvaro Uribe," Mr Correa said on arrival in the Dominican Republic.
For his part, Mr Chavez, a staunch opponent of the Bush administration, alleged that the US was involved in planning and directing the cross-border operation.
He repeatedly accuses the Colombian government, which receives billions of dollars in US aid to fight drug-trafficking, of being a lackey of Washington.
Mr Uribe says he has already apologised to Ecuador and has also called on Colombia's neighbours to do more to stop rebels taking refuge in their territory.
On the eve of the summit, Ecuador announced that it had captured five alleged Farc guerrillas.
Defence minister Gustavo Larrea said the suspected rebels were detained by the army during a search of farms and houses close to the Colombian border.
The Rio Group meeting was scheduled long before the crisis erupted.