"I announce with a tear in the heart: Venezuela breaks off from this moment all relations with the government of Colombia," Venezuelan President Hugo Chavez told reporters in his presidential palace in Caracas.

The announcement marked a fresh spike in tensions between the South American neighbors, which went to the brink of war in 2008 over a Colombian military raid into Ecuador to destroy a cross-border rebel camp.

Colombia, Washingtons staunchest military ally in the region, and Venezuela, a Cuban ally that has accumulated an arsenal of modern Russian warplanes and weapons, have frequently quarreled over the past few years.

The putative help Chavez is accused of giving Revolutionary Armed Forces of Colombia (FARC) guerrillas has fueled much of the ill-will.

Diplomatic relations have been fragile after past downgrades.

Colombia and Venezuela froze diplomatic ties last year after Bogota and Washington inked a military cooperation agreement Chavez considered a threat to regional security.

A mutual loathing between Chavez and Colombian President Alvaro Uribe -- who steps down August 7 to be succeeded by his former defense minister Juan Manuel Santos -- has also aggravated the situation.

Chavezs decision to break ties came in response to Uribes charge that rebels from the FARC and the smaller National Liberation Army (ELN) insurgency group were using Venezuela as a rear base with impunity.

Uribe, in a statement last week, spoke of "the presence in Venezuela of terrorists who are seeking to attack our country."

Four FARC leaders and one from the ELN were in Venezuela, operating from there with impunity, he said, threatening to take the matter to international forums.

On Thursday, the Colombian representative to the Organization of American States, Luis Hoyos, told the Washington-based body that Bogota had evidence of "the consolidated, active and growing presence of these terrorist bands in the brother country of Venezuela."

Showing graphic photos of victims of attacks he said were carried out by Venezuelan-based guerrillas, he said Caracas must "accept its obligation" to bar the rebels from its territory.

Venezuela has strenuously denied the accusations, and last week recalled its ambassador to Bogota to register its anger.

Colombia responded in kind, withdrawing its envoy to Caracas days later.

Chavez said Thursday his decision to cut ties was based on "dignity" in the face of the allegations.

He claimed the outgoing Colombian leader was responsible for the dive in relations, saying: "Uribe is capable of ordering a fake camp be built on the Venezuelan side to attack it and cause a war."

He warned that "we would go crying to a war with Colombia, but we would go."

The United States, commenting on the diplomatic breakdown between Venezuela and Colombia, said Chavezs decision is not the "proper way" to raise concerns.