Ivan Rios, a top leader of FARC, was killed Friday by his own chief of security in what was the second major blow to the country's biggest left-wing rebel group in less than a week, Colombia's government confirmed.

The news threatened to destabilize already strained relations between Colombia and Venezuela following the death of another FARC leader, Raul Reyes, who was killed in a firefight with Colombian government forces last weekend.

Rios' security chief gave Colombian troops the leader's severed hand as proof, the defense minister said Friday.

Ivan Rios was the second top rebel killed in a week, a major setback for the Revolutionary Armed Forces of Colombia, the country's largest rebel force. FARC spokesman Raul Reyes was killed Saturday in a cross-border raid in Ecuador that set off an international diplomatic crisis.

"The FARC has suffered a new, major blow," Defense Minister Juan Manuel Santos said at a news conference.

Santos said troops launched an operation designed to capture Rios on Feb. 17 after receiving tips that he was in a mountainous area of the western province of Caldas.

On Thursday, he said, a guerrilla known as Rojas came to the troops with Rios' severed hand, laptop computer and ID, saying he had killed his boss.

It was unclear what motivated Rojas to kill his boss. Santos did not say what happened to Rojas, and he did not take questions.

The U.S. State Department has a standing bounty of $5 million for Rios' capture.

Local Colombian media showed live pictures from the border where a few Venezuelan troops allegedly crossed into Colombia and fired shots.

Venezuelan President Hugo Chavez has ordered thousands of troops and tanks to Venezuela's border with Colombia and threatened to slash trade and nationalize Colombian-owned businesses.

Ecuador also has sent troops to the border.

Meanwhile, the presidents of Colombia, Ecuador and Venezuela had a heated meeting in the Dominican Republic for a summit of Latin American leaders aimed at calming the crisis triggered by deadly Colombian cross-border raids.

The leaders of the three nations shook hands late Friday, ending a tense debate at the summit over Colombia's raid.

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The leftist presidents of Venezuela and Ecuador kept the pressure on Colombia as they arrived in the Dominican capital late Thursday. The Rio Group summit was to have focused on energy and other issues, but the diplomatic crisis in the Andes now has center stage.

Ecuadorian President Rafael Correa told reporters he wants Colombian President Alvaro Uribe to apologize for Saturday's military attack against leftist Colombian rebels in Ecuadorian territory, as well as his "formal and firm commitment" that Colombia will never "violate" the sovereignty of another country.

Uribe said his military was forced to act because Colombia's neighbors have provided refuge to FARC, or Revolutionary Armed Forces of Colombia, which finances its anti-government insurgency through kidnapping and drug trafficking. And he said that the rebels have responded in kind, doing favors for Chavez and helping Correa get elected.

"Your insolence is doing more damage to the Ecuadorean people than your murderous bombs," Correa responded, bellowing into his microphone. "Stop trying to justify the unjustifiable!"

Correa later drew loud applause when he emphasized that Colombia violated his nation's sovereignty by sending commandos across the border to attack a rebel camp in Ecuador. He portrayed Ecuador as a victim of Colombia's conflict, and proposed an international peacekeeping force to guard their border.

Uribe's speech was met with silence.

Uribe, meanwhile, produced letters between Correa and FARC he claims prove new relations between Ecuador and terrorists, and said Ecuador has not and will not provide information on the FARC terrorists.

Correa called Uribe a liar and left the meeting, with an aide saying it was because he had to use the restroom.

Uribe also denounced the contact between FARC and the Venezuelan military, and called out Chavez for working with and supporting the group, evoking laughter in the Venezuelan leader.

On his arrival in Santo Domingo, Chavez took jibes at Colombia and the United States, which has supported the Andean nation with more than $4 billion in counterinsurgency and anti-drug aid since 2000.

"The U.S. empire has taken over Colombia," Chavez said.

Uribe, who is hugely popular among Colombians for efforts to crack down on FARC, which finances itself through kidnapping and drug trafficking, declined to comment on the crisis as he arrived for a meeting with Dominican President Leonel Fernandez.

Ecuador and Nicaragua have broken diplomatic relations with Colombia.

The standoff underscores Latin America's swerve to the left in recent years — and the increasing isolation of Colombia's center-right government, Washington's strongest ally in Latin America.

Correa, Chavez and Nicaraguan President Daniel Ortega are all strident leftists — and Ortega once was a Sandinista guerrilla fighter who battled a U.S.-backed dictatorship in his homeland in the 1970s. But even centrist leaders lectured Uribe about the need to honor territorial sovereignty and the rule of law.

Chavez struck a conciliatory tone in his speech, noting that the crisis "keeps heating up."

He denied that he had given $300 million to the FARC, as alleged in a letter purportedly written by Raul Reyes, a top rebel leader killed in the attack. Chavez also denied having sent arms to the rebels.

"I have never done it and will never do it," Chavez said. "I could have sent a lot of rifles to the FARC. I will never do it because I want peace."

Then, as Uribe shifted in his chair, Chavez invited in the mother of French-Colombian politician Ingrid Betancourt — the highest-profile hostage held by the rebels — and urged Uribe to allow a multinational group into Colombia to facilitate another hostage release.

Chavez earlier claimed without providing evidence that United States planned, directed and participated in the attack. U.S. Southern Command spokesman Jose Ruiz wouldn't confirm or deny U.S. participation.

The United States has provided billions of dollars in military aid to Colombia and U.S. special forces train Colombian troops. But U.S. soldiers are barred by U.S. law from participating in combat operations and can open fire only to defend themselves.

Uribe held up documents he said were recovered from Reyes' laptop, including one in which the rebel leader told the guerrillas' top commander about "aid delivered to Rafael Correa, as instructed."

Uribe added that he didn't give 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."

After Uribe and Correa finished trading jabs amid references to communism and terrorism, Mexican President Felipe Calderon said he was saddened by the hostility, and that such divisions threaten to set back efforts to improve the lives of Latin Americans.

Guatemala's Alvaro Colom proposed that a reconciliation commission visit both countries. And Argentina's Cristina Fernandez called for a return to "legality," rejecting unilateral actions by any country.

Uribe, who held up his finger while lecturing his neighbors about the danger of the FARC, suggested that Correa was dishonest about his efforts to go after Colombian rebels on Ecuadorean soil.

Correa shook his head, then smiled. Uribe bristled.

"Regarding your smile President Correa, I tell you that we have no interest in hiding anything," Uribe snapped.

One of the rare regional voices offering support for Colombia was Salvadoran President Tony Saca, who said the Colombian government should be able to defend its citizens.

"We need to understand Colombia has the legitimate right to go after terrorists ... wherever they may be, of course without harming the sovereignty of another country," Saca said on arrival in Santo Domingo.

FOX News' Adam Housley and The Associated Press contributed to this report.