CARACAS, Venezuela — President Nicolás Maduro pushed ahead Sunday with the controversial vote for a powerful constitutional assembly amid protests that left a dozen people dead, according to opposition officials, who led a massive boycott of the polls.

The beleaguered South American nation is electing members to the new assembly that would rewrite the country’s 1999 constitution and possibly create a single-party, authoritarian system.

Julio Borges, president of the opposition-led National Assembly, said only 7% of the electorate had voted — a silent protest of Maduro's power grab, which would slam the brakes on democracy.

A mid-day check of 10 polling places here in the capital showed most of them empty or nearly empty.

“Venezuela has screamed with its silence,” said Borges, who put the day's death toll at 12. The public prosecutor's office confirmed nine deaths.

Around 6 p.m., National Electoral Council Vice President Sandra Oblitas extended voting until 7 p.m. amid what she said were reports of difficulties voting in some areas because of people blocking access to polling places.

Maduro's vision of a new constitution to consolidate his power has drawn ire in Washington. Last week, the Trump administration imposed sanctions on 13 senior Venezuelan officials, and the White House and some U.S. lawmakers said stiffer sanctions could follow. Mexico said it would support U.S. sanctions, and the Organization of American States and the European Parliament have also expressed support for the opposition.

In Venezuela, opposition leaders refused to put up candidates, arguing that the election has been structured to ensure that Maduro’s ruling socialist party dominates. Thus virtually all the more than 5,000 candidates for 545 assembly seats are Maduro supporters.

The opposition vowed to protest despite a ban on public gatherings issued by Maduro. In some parts of the capital, people took to the streets in protest against the vote, but they were soon repelled by security forces throwing tear gas.

During a protest, opposition supporters set an explosive that injured seven police officers, the public prosecutor's office said. After the blast, police set fire to four motorcycles belonging to journalists.

Opinion polls indicated more than two-thirds of the nation opposed the president's efforts, and voting at many polling places was light. The opposition says the government was so afraid of low turnout that it threatened to fire state workers who don’t vote and take away social benefits like subsidized food from recipients who stay away from the polls.

“I’m here because I’m hoping for housing,” admitted hairdresser Luisa Marquez, 46, as she waited in line to vote.

Maduro has struggled with a rapidly deteriorating economy and strengthening political opposition. Some voters said they believed the new assembly might improve life in Venezuela.

“I’m voting today because I want peace to be restored,” said seamstress Carmen Martinez, 44. But she said she was less certain the assembly will solve the nation's economic ills.

"I’m going to have hope, but I doubt this could solve that problem," she said.

Months of violence leading up to the vote showed little signs of ending, with media reporting that a leading assembly candidate and an opposition activist were killed before voting even began.

José Felix Pineda, a lawyer running in the election, was shot in his home Saturday night, a senior Venezuelan minister told the BBC.

Maduro has denied links to violent paramilitaries that have run roughshod across the country, blaming the opposition for unrelenting violence that has left more than 100 people dead.

Maduro himself voted with little fanfare early in the morning.

“We’ve stoically withstood the terrorist, criminal violence,” he said. “Hopefully the world will respectfully extend its arms toward our country.”

Contributing: John Bacon in McLean, Va.