The U.S. government has sanctioned Venezuelan President Nicolas Maduro for undermining democracy, following Sunday's constitutional assembly elections, and said all of his assets subject to U.S. jurisdiction would be frozen.

Americans would also be prohibited from transactions with Maduro, according to a Treasury Department edict issued Monday afternoon.

Maduro's government says the election gives the assembly a popular mandate to dramatically recast the country's political system, even as condemnations of the process have poured in from nations abroad and opponents at home.

Henrique Capriles, opposition leader and governor of the central state of Miranda, urged Venezuelans to protest Monday against an assembly that critics fear will effectively create a single-party state.

Maduro has said the new assembly will begin to govern within a week. He said he would use the assembly's powers to bar opposition candidates from running in gubernatorial elections in December unless they sit with his party to negotiate an end to hostilities that have generated four months of protests, killed at least 125 and wounded nearly 2,000.

Venezuela's chief prosecutor's office reported 10 deaths in new rounds of clashes Sunday between protesters and police. Seven police officers were wounded when a fiery explosion went off as they drove past piles of trash that had been used to blockade a street in an opposition stronghold in eastern Caracas.

At least 10 people were killed during violent clashes between demonstrators and police during Sunday's Venezuelan vote. (Carlos Garcia Rawlins/Reuters)

Maduro said a new constitution is the only way to end such conflicts.

"The people have delivered the constitutional assembly," Maduro said on national television. "More than eight million in the middle of threats … it's when imperialism challenges us that we prove ourselves worthy of the blood of the liberators that runs through the veins of men, women, children and young people."

But the chief prosecutor, a longtime government loyalist who broke with Maduro in March, said in a speech Monday that the new assembly that is supposed to rewrite the constitution will put "absolute power" in the hands of a minority certain to abolish essential political rights like the freedom of expression.

Luisa Ortega Diaz said that Venezuela is now run by a state with "dictatorial ambitions."

Maduro called the vote for a constitutional assembly in May after a month of protests against his government, which has overseen Venezuela's descent into a devastating crisis during its four years in power. Due to plunging oil prices and widespread corruption and mismanagement, Venezuela's inflation and homicide rates are among the world's highest, and widespread shortages of food and medicine have citizens dying of preventable illnesses and rooting through trash to feed themselves.

Core of loyal supporters remain

National electoral council president Tibisay Lucena announced just before midnight that turnout in Sunday's vote was 41.53 per cent, or 8,089,320 people. Members of the opposition said they believed between two million and three million people voted.

Turnout in the 2013 presidential election was 80 per cent. Maduro received 7.6 million votes, enough for a narrow victory.

Venezuela's President Nicolas Maduro speaks to supporters in Caracas on Sunday. (Miraflores Palace/Reuters)

"If it wasn't a tragedy … if it didn't mean more crisis, the electoral council's number would almost make you laugh," opposition leader Freddy Guevara said on Twitter.

Maduro has threatened that one of the constitutional assembly's first acts would be jailing Guevara for inciting violence.

Maduro blasts 'emperor' Trump

Nations including Argentina, Canada, Colombia, Mexico, Panama, Paraguay, Spain, Britain and the United States said they would not recognize Sunday's vote.

The U.S. government did not include oil-related sanctions in their announcement Monday, but such measures remain under consideration, congressional sources and a person familiar with the matter told Reuters.

After the announcement, an official told Associated Press that Trump's administration held off on sector sanctions due to possible complications, including some involving subsidiaries. The official wasn't authorized to speak publicly on the process and demanded anonymity.

Trump's national security adviser, H.R. McMaster, described the election as an "outrageous seizure of absolute power" that "represents a very serious blow to democracy in our hemisphere."

"Maduro is not just a bad leader, he is now a dictator," McMaster said.

The European Union also condemned the process.

"Venezuela has democratically elected and legitimate institutions whose role is to work together and to find a negotiated solution to the current crisis," the statement said. "A Constituent Assembly, elected under doubtful and often violent circumstances, cannot be part of the solution."

Canada denounces & condemns significant and undemocratic action by <a href="https://twitter.com/hashtag/Venezuela?src=hash">#Venezuela</a> gov to create constituent assembly <a href="https://t.co/SYsATMAXDz">https://t.co/SYsATMAXDz</a> <a href="https://t.co/qTJrBiKWOX">pic.twitter.com/qTJrBiKWOX</a> —@CanadaFP

Maduro was defiant in the face of U.S. opposition hours before the sanctions were announced.

"A spokesperson for Emperor Donald Trump said that they would not recognize the results of Venezuela's constituent assembly election," he said to cheering supporters. "Why the hell should we care what Trump says? We care about what the sovereign people of Venezuela say."

After the U.S. announcement, Maduro said on national television, "The threats and sanctions of the empire don't intimidate me for a moment." He also told viewers, "I don't listen to orders from the empire, not now or ever.... Bring on more sanctions, Donald Trump."

Maduro said he had received congratulations from the governments of Cuba, Bolivia and Nicaragua, among others.

'The government has suffered a defeat today'

Opposition leaders had called for a boycott of the vote, declaring it rigged for the ruling party. Ahead of the vote, the opposition organized a series of work stoppages, as well as a July 16 protest referendum that it said drew more than 7.5 million symbolic votes against the constitutional assembly.

Clashes continued throughout Sunday, as the controversial vote proceeded despite large protests in the capital of Caracas and other cities around Venezuela. (Andres Martinez Casares/Reuters)

"It's very clear to us that the government has suffered a defeat today," said Julio Borges, president of the opposition-controlled but largely powerless National Assembly. "This vote brings us closer to the government leaving power."

The winners among the 5,500 ruling-party candidates running for 545 seats in the constituent assembly will have the task of rewriting the country's constitution and will have powers above and beyond other state institutions, including the opposition-controlled congress. Maduro has said the assembly's new draft constitution must then be approved in a referendum.