Venezuelan authorities have vowed to investigate the killing of a 19-year-old man during anti-government demonstrations, the first protest death since a controversy over the Supreme Court began.

Thousands of Venezuelan opponents of President Nicolas Maduro’s socialist government marched to protest a decision by the administration-leaning top court to assume control of the opposition-led congress in what demonstrators said was a lurch toward dictatorship.

While the widely condemned decision was quickly overturned, the opposition has stepped up street protests against Mr Maduro, even though such demonstrations have achieved little in the past.

Thursday’s march culminated in clashes, and opposition leaders said Jairo Ortiz was shot in a Caracas suburb that night by security forces that were breaking up a protest there.

The state prosecutor’s office confirmed on Friday that Mr Ortiz was shot in the hilly, low-income Carrizal area of capital Caracas, known for its state-provided housing, while he was at a protest.

“Officials of the Bolivarian National Guard and the Bolivarian National police approached the area,” the office said in a statement, adding it would investigate the incident.

“During this situation, Ortiz... received a bullet that caused his death.”

Local media reported Mr Ortiz was a university student planning to emigrate from Venezuela, like so many in the middle class that have fled to Colombia, Panama, Chile or the US city of Miami amid the economic crisis and political turmoil.

A galvanised opposition, buoyed by the latest international outcry against Mr Maduro, is planning another protest in Caracas on Saturday. Legislators gathered on Friday in front of the state human rights ombudsman’s office at dawn, wrapping red tape emblazoned with the words “danger, do not enter” around the building in a surprise protest.

“We declare this office closed because it’s back is to the people,” tweeted opposition legislator Milagros Paz.

“Jairo Ortiz died in the hands of this regime.”

The opposition, which accuses ombudsman Tarek Saab of being an extension of Mr Maduro’s government, was blocked on Thursday from marching to the ombudsman’s office. Mr Saab condemned Mr Ortiz’s death on Friday, calling it a “vile assassination”.

It came as opposition leader and two-time presidential candidate Henrique Capriles said on Friday that he had been banned from holding political office for 15 years, amid what critics say is a crackdown on dissent by the leftist government.

Over the last few days, authorities have accused Mr Capriles of fomenting violence and bloodshed by leading protests against Mr Maduro.

A ban on holding office would prevent Mr Capriles from running for president again in elections currently scheduled for late 2018.

“URGENT: I inform the country and international public opinion that I am being notified at this very moment of a BAN for 15 years,” tweeted Mr Capriles, who is currently the governor of the central coastal state of Miranda.

There was no immediate comment from authorities.

The Mr Capriles decision will likely stoke tensions in Venezuela, where more than 100 political prisoners are now being held, according to the opposition and rights groups.

Fellow opposition leader Leopoldo Lopez, Venezuela’s best-known prisoner, was himself barred from office in 2008, when he was the popular mayor of a Caracas district.

Mr Lopez had been expected to challenge late leader Hugo Chavez in the 2012 presidential election but handed the baton over to Mr Capriles, who lost that vote and another against Mr Maduro in 2013 after Mr Chavez’s death.

“Mr Capriles, you’re trying to ignite the country,” Socialist Party official Freddy Bernal said during a government rally on Thursday.

“You’re looking for deaths. Don’t then come like a sissy saying that you’re a political prisoner. Don’t then come crying that you’re being persecuted.”

Mr Maduro’s government has said foreign-backed opposition lawmakers are seeking to agitate protesters in hopes of stoking a coup to get their hands on Venezuela’s crude oil reserves, the world’s largest.

Mr Maduro said in a televised address on Thursday that authorities had detained 30 people involved in the demonstration.