Maduro faces mounting accusations at home and abroad of trampling on democracy with his "Constituent Assembly," elected Sunday in a vote boycotted by the opposition and allegedly marred by fraud.
The 545-member assembly -- whose members include Maduro's wife and son -- was initially due to start work today. The opposition Democratic Unity Roundtable (MUD), which holds a large majority in congress, had called for a major protest in Caracas on the same day.
Venezuela is in the grips of four months of violent protests that have left more than 125 people dead as opposition demonstrators armed with stones and Molotov cocktails battle the security forces and armed motorcycle gangs of Maduro supporters.
Despite the protests and international condemnation, Maduro insists the new assembly is the solution to a drawn-out economic and political crisis gripping Venezuela, whose 18- year-old, oil-fueled socialist economic model has been driven to the brink of collapse by a plunge in global crude prices.
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The United States imposed direct sanctions on Maduro, calling him a "dictator," while the European Union joined the US, Mexico, Colombia and Argentina in saying it would not recognize the new assembly.
In the latest attack on the election, Attorney General Luisa Ortega, one of Maduro's most outspoken critics, opened an investigation into what she called scandalous electoral fraud.
The allegation came from a British technology firm hired to handle the vote, Smartmatic. It says the official figures from the election were tampered with to make turnout appear greater than it was.
Maduro denied the accusation, dismissing it as a "reaction by the international enemy."
Smartmatic chief executive Antonio Mugica said the firm had concluded "without any doubt" that turnout was manipulated.
"We estimate the difference between the actual participation and the one announced by authorities is at least one million votes," he said.
Venezuela's pro-government electoral authority had claimed more than eight million voters took part -- 40 percent of the electorate.
The opposition says turnout was closer to 3.5 million, mostly state employees fearful for their jobs.
More than 70 percent of Venezuelans oppose the new assembly, according to polling firm Datanalisis.
Because of an opposition boycott, it was a foregone conclusion that followers and allies of Maduro's Socialist Party would fill all the Constituent Assembly posts. So the turnout figure was the key gauge of public support.