The demonstrations will help measure support for the leader of the opposition-controlled National Assembly, who is recognized by more than 50 countries as Venezuela's interim president, since the April 30 attempt to oust Maduro fizzled.

Guaido has faced a number of setbacks: his deputy Edgar Zambrano was arrested by Maduro's SEBIN intelligence service and is being held for "the flagrant commission of the crimes of treason, conspiracy and civil rebellion," the Supreme Court said.

Three other lawmakers have sought refuge in various diplomatic installations in Caracas, and one fled to neighboring Colombia.

"This Saturday, we will take to the streets for our National Assembly... for our brave lawmakers who are giving everything they have and for an entire nation that remains mobilized to win its freedom," Guaido tweeted late Friday.

Crowds started forming in a neighborhood of eastern Caracas that mainly supports the opposition. Guaido greeted supporters and was expected to speak.

"Guaido cannot do it alone. Everyone must come out and protest," said Daisy Montilla, 69, who carried the Venezuelan flag.

Guaido and Maduro have been battling each other for months, ever since the 35-year-old lawmaker declared himself acting president, against a backdrop of the country's spiraling economic crisis, which has led to basic food and medicine shortages.

Guaido, who says Maduro rigged his own re-election last year, has repeatedly led street demonstrations and has called on the military to turn their backs on Maduro, who is supported by China and Russia.

So far, the armed forces have remained in Maduro's corner, except for around 30 military personnel who heeded Guaido's call for an uprising last month.

That abortive attempt to unseat Maduro, the political heir of the late Hugo Chavez, led to unrest that left six people dead.

On Friday, Maduro accused his sacked intelligence chief of being a CIA "mole" and the architect of the failed military uprising.

"He was captured by the CIA a year ago and was working as a traitor, mole and infiltrator," Maduro said of Cristopher Figuera, whose defection to the opposition saw him rewarded earlier this week by the US, which removed him from its sanctions list.

Figuera and 55 other officers have been expelled from the Venezuelan armed forces.

Zambrano -- who is being held in a military prison -- is one of 10 opposition lawmakers charged with treason by the Supreme Court for participating in the April 30 movement.

One of the other charged lawmakers, Luis Florido, announced in a video on Friday that he had fled to neighboring Colombia, "sheltered from a regime that is willing to imprison deputies," he said.

Three others -- Richard Blanco, Mariela Magallanes and Americo De Grazia -- have sought refuge in the residences of the Argentine and Italian ambassadors in Caracas.

Guaido said on Thursday the arrests were part of a bid by Maduro to dismantle the National Assembly legislature, Venezuela's sole opposition-controlled institution but one which had already been rendered powerless by the pro-Maduro Supreme Court.

"The National Assembly was elected by popular vote. (The government) cannot dissolve it by persecuting lawmakers as it's doing now," said one protester in Caracas, Alexander Mendoza.

The United States and the European Union have condemned the Maduro government's actions against opposition lawmakers.

On Friday, Washington imposed sanctions on two shipping companies for delivering Venezuelan oil to ally Cuba, in what it said was a response.

In an interview with Portuguese television aired Saturday, Guaido said a foreign military intervention could only happen when it is the "last option."

US President Donald Trump has said all options remain on the table.

Separately on Friday, Venezuela announced it was reopening its land border with Brazil. That border was closed in February, frustrating Guaido's attempt to bring stockpiled humanitarian aid, mostly from the US, across the border.

However, the border with Colombia and links with other parts of the former Dutch Antilles will remain shut, Vice President Tareck El Aissami said.

The United Nations says a quarter of Venezuela's 30 million people are in urgent need of aid, and more than 2.7 million have fled the deprivation.