Venezuela will hunt down and jail leaders of violent protests, its new top prosecutor said, a day before a hate crimes law is expected to be approved despite fears it will be used to crush dissent.

Tarek Saab, appointed by the new Constituent Assembly early this month, vowed to track down the leaders of demonstrations, in which more than 120 people have died since the start of April.

"It will be a point of honour for the public prosecutor's office to identify who was responsible for each of the hate crimes that occurred in this country," Saab, Maduro's ex-human rights ombudsman, shouted during a speech to the assembly on Thursday.

"We will search the cameras, videos, photographs. We will get images of each one of them to make sure they pay for having killed, for having hurt people and left orphans behind," he said to a standing ovation by the Socialist Party-dominated assembly.

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The new law "against hate and intolerance" - denounced by rights groups as a sham aimed at persecuting the opposition - was set to be approved on Friday by the new legislative superbody elected last month at the behest of President Nicolas Maduro.

Maduro loyalist Delcy Rodriguez, head of the Constituent Assembly, said the law would be passed before the weekend.

The international community, however, has pointed at the Maduro government, not opposition demonstrators, when assigning blame for the majority of deaths.

Venezuelan security forces and pro-government groups are believed to be responsible for at least 73 demonstrator deaths since April, the United Nations said in an August 8 report.

Abuses of protesters, including torture, were part of "the breakdown of the rule of law" in the oil-rich but economically ailing nation, the report said.

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Those found guilty of expressing hate or intolerance will be punished with up to 25 years in jail, according to the vaguely worded hate crimes bill.

Groups such as Human Rights Watch say it would give Maduro's government carte blanche to take opposition leaders out of circulation ahead of October's gubernatorial elections.

The assembly has established a truth commission to investigate opposition candidates to ensure any involved in violent protests would be barred from running for governorships, Rodriguez said.

The opposition - which won control of Congress in 2015 only to see its decisions nullified by Maduro's loyalist Supreme Court, boycotted the July 30 election of the Constituent Assembly. The body has sweeping powers to rewrite Venezuela's constitution and even permit Maduro to rule by decree.