Opponents of embattled President Nicolas Maduro vowed another day of nationwide marches, defying an intensifying crackdown on protests that have left more than 120 people dead in four months.

Flouting international condemnation -- including the threat of new sanctions by US President Donald Trump's administration -- Maduro meanwhile claimed victory in Sunday's election, citing an official turnout figure of 41.5 percent.

The leftist leader encouraged the new "Constituent Assembly" to wield its vast powers to scrap opposition lawmakers' immunity from prosecution as one of its first acts.

Protesters attacked polling stations and barricaded streets around the country on Sunday, drawing a bloody response from security forces, who opened fire with live ammunition in some cases.

Despite the unrest and an opposition boycott, the National Electoral Council said there had been "extraordinary turnout" of more than eight million voters.

Dressed in bright red, his fist clenched and face beaming, Maduro hailed it as a win in a speech to hundreds of cheering supporters in central Caracas early Monday.

"It is the biggest vote the revolution has ever scored in its 18-year history," he said, referring to the year his late mentor, Hugo Chavez, came to power.

"What the hell do we care what Trump says?"

Members of the new assembly will include his wife Cilia Flores, his pugnacious right-hand man Diosdado Cabello, and other staunch allies.

The socialist president is gambling his four-year rule on the 545-member assembly, which will be empowered to dissolve the opposition-controlled congress and rewrite the constitution.

There was blistering international condemnation of the vote, led by Washington.

The constituent assembly aims to "undermine the Venezuelan people's right to self-determination," US State Department spokeswoman Heather Nauert said in a statement.