Mr. Maduro was sworn in for a second term as president on Thursday, after an election that was widely denounced by other countries as fraudulent. During his six years in office, the country’s economy has unraveled, leading to widespread hunger and violence. An estimated three million people have fled Venezuela since the crisis took hold.

On Friday, Mr. Guaidó, 35, called for Venezuelans to take the streets in protest against Mr. Maduro’s continuing rule, and asked the armed forces to support his becoming interim president while new elections are held.

Mr. Guaidó argued that the Constitution gave him “the legitimacy to carry out the charge of the presidency over the country to call elections,” adding: “But I need backing from the citizens to make it a reality.”

Mr. Maduro accused the opposition leader of trying to stir dissent.

The National Assembly, which Mr. Guaidó leads and which is controlled by lawmakers who oppose Mr. Maduro, was essentially nullified in 2017 when the president created a new Constituent Assembly. That body, which was given broad powers to write and pass legislation, is controlled by supporters of Mr. Maduro.