The "amnesty law" would extend also to civilian government officials who collaborate "in the restitution of constitutional order," parliament said.

"We're talking to middle and low-ranking military: break away from the fear," said parliamentary president Juan Guaido, who last week branded Maduro a "usurper."

The row between the legislature and Maduro has intensified since the socialist leader was sworn in last week for a second term of office in the crisis-hit country, after he won snap elections in May that were boycotted by the opposition and dismissed by the United States, European Union and Organization of American States as a fraud.

Guaido was briefly detained on Sunday by intelligence service agents but Maduro claimed on Monday that the incident had been staged by the opposition alongside rogue officers whom he says have since been dismissed.

He also vowed: "I won't tremble before anyone!"

Crucially, Maduro has the backing of the military high command.

As the National Assembly held its session, he appeared on a radio and television station alongside defense minister General Vladimir Padrino.

"We are ready to die, as we have vowed, to defend the constitution," said Padrino.

"The people made you supreme magistrate and constitutional president."

Maduro was sworn in on Thursday by the Supreme Court rather than the National Assembly, as stipulated in the Venezuelan constitution.

The legislature has been left powerless by Maduro after he lost control of the National Assembly in parliamentary elections in 2016. Maduro quickly appointed loyalists to the Supreme Court, which in 2017 stripped parliament of its powers.

Maduro then created the Constituent Assembly to replace parliament, with the new body subsequently declaring itself the supreme branch of government.

However, Guaido insists that Venezuela's constitution gives him the authority to assume power as part of a transitional government and has urged the population and military to take to the streets in support of such a move.

He has called for a mass protest on January 23.

Maduro, though, warned ominously that "the courts will put everything in place."

In a telephone call with Guaido, US Vice President Mike Pence reiterated Washington's position that the National Assembly, is "the only legitimate democratic body" in Venezuela, the White House said.

Pence added that the goal of the US -- which has sanctions against Venezuelan officials -- "is to restore democracy to Venezuela through free and fair elections, and end the unprecedented humanitarian and economic crises."

He encouraged Guaido "to build unity among political groups," the White House said.

Maduro is widely blamed for Venezuela's economic crisis, which has forced millions to flee a country where basic food and medicines are scarce, and hyperinflation is estimated to reach 10 million percent in 2019, according to the International Monetary Fund.

He has accused Washington of encouraging a coup d'etat in his country.