"He is a puppet, an American agent, created by… the US intelligence agencies, it is them who control him", Maduro told Venezuela's state television.
Guaido assumed the presidency of the National Assembly last week.
Current Venezuelan President Nicolas Maduro will be sworn in for a second six-year term on 10 January before the country's Supreme Court and not before the National Assembly.
Maduro won the 20 May 2018 elections, which have been widely condemned as illegitimate. At a meeting in Peru on Friday, the Lima Group of Latin American countries plus Canada denounced Maduro's second term.
In December, Maduro said he had instructed the country's Armed Forces to maintain the highest level of combat readiness to defeat "imperialistic plots".