President Chavez has often denounced what he called US-backed plans to assassinate him. American officials deny the claims as populist rhetoric meant to increase support at home, and the CIA has dismissed the latest accusation.

Nicolas Maduro, a Chavez ally and president of the National Assembly, said that he planned to file charges with the attorney-general and military prosecutors "of a plot orchestrated by the CIA against the Venezuelan democracy".

But Paul Gimigliano, a CIA spokesman, said: "It's nonsense."

Maduro gave no details about what the CIA involvement may have been. Pro-Chavez legislators played taped conversations which they said were of retired and active army officers conspiring to murder Chavez and other state officials and foment violent riots.

"They planned to suspend the elections," Maduro said. "They planned to attack the head of state, assassinate top officials and carry out massive killings - all these charges are backed up by conversations between the very participants."

Government officials also said that an explosion at an oil pipeline before polls opened for the election on Sunday had been sabotage.

Evidence promised

Opposition leaders, who boycotted Sunday's election and handed pro-Chavez lawmakers control of the National Assembly, have dismissed the election sabotage charges as fabrications meant to discredit them.

Henry Ramos, leader of Democratic Action, said: "No one has any plans in the democratic opposition to kill Chavez, to overthrow his government or to mess around with the barracks, in fact it is exactly the opposite."

The pro-Chavez lawmakers presented no proof of US involvement, saying only that "it was obvious" that financing of weapons purchases came from the US. They promised to present evidence to support their claims on Saturday.

Officials said that plotters were trying to buy grenades, rocket launchers and assault rifles, as well as trying to convince military officers to disobey the government and take their units, including tanks, to the streets.

US officials portray President Chavez, a former paratroop officer and an ally of Cuba - who has become the region's fiercest critic of President Bush - as an authoritarian menace to democracy in Venezuela and South America.

Chavez, who was elected in 1998, has previously accused Washington of involvement in a failed coup against him in 2002.

Despite their differences, Venezuela is still one of the main suppliers of oil to the US. It is the world's fifth-biggest crude exporter.