Venezuelan President Nicolas Maduro warned on Wednesday that he would be "ruthless" with the opposition if they attempted a coup d'etat, after his government said it had thwarted a plot to assassinate him.

"We would be ruthless in a revolutionary counteroffensive against a attempted fascist coup - ruthless!" an agitated Maduro said in an address broadcast nationwide on radio and television.

Earlier, Maduro's spokesman Jorge Rodriguez said on state television that a network of mostly retired police officers and soldiers planned to bomb a key government building, seize a Caracas airbase and loot Venezuela's central bank.

He also said the plotters wanted to edge opposition leader Juan Guaido out of Venezuela's political landscape.

Guaido, leader of the opposition-dominated National Assembly, is seeking to remove Maduro from power with backing from more than 50 nations. In January, he invoked the constitution to declare himself interim president, calling Maduro's 2018 re-election illegitimate.