Ecuador has cut diplomatic ties with Colombia in a deepening crisis over a cross-border raid by Colombian troops.
Venezuela also said it was expelling all Colombian diplomats in the wake of the raid, which killed senior Farc rebel Raul Reyes and 16 others.
Venezuela and Ecuador have deployed troops to their borders amid calls for restraint led by†the head of the UN.
Ecuador said the raid had scuppered a possible deal to free French-Colombian Farc hostage Ingrid Betancourt.
President Rafael Correa said his government had been in "very advanced" talks to release the ex-Colombian presidential candidate, who has been held for six years, and other hostages.
Latin American powers including Chile, Mexico and Brazil have offered to mediate in the dispute. An emergency meeting of the Organization of American States will be held on Tuesday to discuss the crisis.
Farc - the Revolutionary Armed Forces of Colombia - has been fighting for more than four decades with the declared aim of a fairer wealth distribution in Colombia.
They fund themselves largely through the cocaine trade, analysts say, while holding hundreds of kidnapped hostages for ransom and political ends.
Ecuador, which had already withdrawn its ambassador from Bogota and expelled Colombia's from Quito, announced on Monday it would sever all diplomatic ties over the cross-border raid.
Shortly afterwards, Venezuela announced the Colombian ambassador and all other diplomats were being thrown out.
Ecuador has been flying troops by helicopter towards the border area, while Venezuela's President Hugo Chavez said he was deploying tanks and troops on Venezuela's border with Colombia.
As the crisis deepened, UN Secretary General Ban Ki-moon added his voice, expressing concern about "increased tensions and heightened rhetoric" in the region.
In Washington, a state department spokesman backed Colombia's right to defend itself while urging dialogue.
Meanwhile, Colombia accused Ecuador and Venezuela of having ties with the Farc and said the rebels had tried to buy uranium.
The Colombian authorities said the information had come from documents found during Saturday's raid on the rebel camp in Ecuador.
"When they mention negotiations for 50 kilos of uranium, this means that the Farc are taking big steps in the world of terrorism to become a global aggressor. We're not talking of domestic guerrilla but transnational terrorism," said Colombian national police chief Oscar Naranjo at a news conference in Bogota.
Other documents showed that President Chavez had provided $300m (£151m) to the Farc, and had received funds from them many years earlier, he said.
And there was also evidence of links between the Farc and representatives of the Ecuadorean government, Gen Naranjo claimed.
But Venezuela and Ecuador poured scorn on the Colombian claims.
HAVE YOUR SAY
Colombia and President Uribe have been fighting a civil war for 40 years, and it's pretty bad. Mr Uribe is trying very hard but these fallouts with other nations are dangerously ignorant and harmful to the region.
Alex Dominguez, Milwaukee
Venezuelan Vice-President Ramon Carrizalez said: "We are accustomed to the lies of the Colombian government. Whatever they say has no importance."
Ecuador's President Correa also criticised Colombia, saying: "They said we had a pact with terrorists, and that is completely false."
Colombia's foreign minister earlier said he regretted that troops had to cross the border, but said it had been necessary "in the fight against terrorism".
"The Colombian government has never wanted to disrespect or violate the sovereignty or integrity of the sister republic of Ecuador," Fernando Araujo said.
Meanwhile, French Foreign Minister Bernard Kouchner said the death of rebel leader Reyes was "bad news", as he had been France's contact in its efforts to free Ms Betancourt.
Venezuelan President Chavez's government also said he had been close on several occasions to a deal to free Ms Betancourt, who is said to be in very poor health.
Six Farc hostages have been released since Mr Chavez began efforts to win their freedom.
Colombia initially invited him to mediate, but later tried to exclude him from the process.