Deal dominates summit
The Unasur meeting was primarily concerned with the handover of the bloc's leadership from Michelle Bachelet, Chile's president, to Raphael Correa, who was sworn in as Ecuador's president for a second term on Monday.
"Colombia thinks this is not a threat to anybody, while Chavez and Raphael Correa both said that letting the US use those bases does represent a threat - not only to Venezuela and Ecuador, but all the Unasur members"
Dima Khatib, Al Jazeera's correspondent in Quito
But Chavez's criticism of the US-Colombia dominated the summit, Dima Khatib, Al Jazeera’s correspondent in Quito, said.
"President Chavez of Venezuela, just before the group photo opportunity, broke the protocol and decided to speak about Colombia," she said.
"The vice foreign minister of Colombia defended the decision to find an agreement with the US on the military bases - he said that the bases are not going to be US bases; they are Colombian bases that would be used by the US.
"Colombia thinks this is not a threat to anybody, while Chavez and Raphael Correa both said that letting the US use those bases does represent a threat - not only to Venezuela and Ecuador, but all the Unasur members."
Washington's plans to send troops to seven Colombian military bases has also been questioned by Bolivia, Chile, Cuba and Brazil.
Chavez has called on governments across South America to sanction Colombia, who he accused on Sunday of recently sending an army patrol into Venezuelan territory.
Bogota has said that no such mission took place.
Colombia has had at least $5bn in mostly military aid from Washington in recent years to help combat drug smugglers and the Revolutionary Armed Forces of Colombia (Farc), a left-wing armed group.
The Colombian government has on several occasions accused Chavez of providing help to the Farc, claims that the Venezuelan leader has repeatedly denied.
Venezuela recalled its diplomats from Colombia in July as relations between the two nations deteriorated.
But trade between the countries has grown, with Venezuela buying Colombian farm produce and cars while exporting fuel and chemicals to its neighbour.