BBC News, Caracas
Two leading Venezuelan MPs have accused the US State Department, the CIA and a Congresswoman of a plot to damage the government of President Hugo Chavez.
Mr Maduro said he had tapes to prove the claims
They said there had been a conspiracy to turn last week's congressional elections in Venezuela into a fiasco.
The claims were made by the speaker of Venezuela's parliament Nicolas Maduro and his wife, Cilia Flores.
A US embassy spokesman in the Venezuelan capital, Caracas, categorically denied all charges.
The allegations were directed at the US embassy in Caracas and Florida's Republican Congresswoman Ileana Ros-Lehtinen.
Mr Maduro and Mrs Flores said they had audio tapes proving that members of Venezuela's opposition living in Miami were undercover agents of the CIA and had been secretly plotting to scupper last weeks parliamentary elections.
They said the recordings were of two Venezuelan women discussing the use of the diplomatic mailbag of the US embassy as a safe channel of communication.
The parliamentarians - who are senior supporters of Mr Chavez - also said Ms Ros-Lehtinen was closely linked to the alleged plotters and was assisting in the conspiracy to overthrow the government.
But the US embassy spokesman told the BBC the US was obeying all diplomatic norms.
Since last Sunday's elections which were boycotted by almost all the Venezuelan opposition parties, President Chavez and his followers have been accusing US diplomats of holding secret meetings with the opposition and foreign election monitors from the European Union and the Organisation of American States.
Although Mr Chavez's supporters say they have won all 167 seats, 75% of Venezuelan's voters abstained from the elections.