Fresh out of his victory in an election ridiculed as a farce by the United States and other countries, he advanced his inauguration for eight months and swore on Thursday for a second six-year term.
Mr. Maduro won an early election on Sunday over a former member of his Socialist Party, having prevented two popular opposition leaders from fleeing and forcing others into exile. Inaugurated before the National Constituent Assembly, a body created by its allies to replace the congress controlled by the opposition, Maduro defended his victory.
"Venezuela had free, legitimate elections," he told his supporters in the ornate precinct of the Congress where the inauguration ceremony took place.
The ceremony was raised in the face of sharp criticism of the election of opposition groups and of many governments around the world, including the Trump administration, which responded by expanding the ban on Americans buying Venezuelan debt.  "He thinks that swearing himself early guarantees six more years," he said.
a former leader of the opposition coalition of political parties. "That's why he urgently sought this legal framework to rescue governance in the future."
Mr. Maduro's enemies noted that under the constitution, the inaugurations must be scheduled for January 10 and presented to Congress, known as the National Assembly. The president of that chamber,
He said that the National Constituent Assembly, the body created by Mr. Maduro's allies, is illegal and was designed to usurp the powers granted to members of Congress.
"By swearing before the Constituent Assembly he is sending the message that he is taking power by force and that he does not abide by the constitution," Barboza said.
The government said that a second inauguration would take place in January, without explaining why.
Mr. Maduro's oath came amid intense tensions with the United States. On Tuesday, Mr. Maduro ordered the chief US diplomat in Caracas, Charge d'Affaires
and his deputy to leave the country. The State Department of the United States responded Wednesday by ordering the departure of two Venezuelan diplomats outside the country.
"We will continue to press the illegitimate regime of Venezuela until democracy is restored", Vice President
He said on his Twitter account.
American hostility is one of the many problems Maduro faces. Your country is falling further into the crisis, hit by hyperinflation, an economy that is almost 50% smaller than in 2013 and the exodus of hundreds of thousands of its compatriots. Oil production now stands at 1.4 million barrels per day, compared to more than three million barrels per day in the late 1990s.
In his inauguration speech, Mr. Maduro was open to the reforms. He said his government would enter into "a process of dialogue and peace" and that some Venezuelans imprisoned for what rights groups call political crimes would be released if they had not committed "serious crimes such as homicide."
"I want those people to be liberated and given an opportunity," he said.
He also acknowledged that there were problems in Venezuela and that "we have to change the country." His answer, he said, is to deepen the socialism started by his mentor and predecessor,
"Venezuela has once again ratified its path, socialism," said Maduro. "You have chosen a president to build socialism, to solve problems, for dialogue and peace."
-Maolis Castro in Caracas contributed to this article.
Write to Juan Forero at Juan.Forero@wsj.com