CARACAS (Reuters) - A man describing himself as a former boss and friend of Venezuelan President Nicolas Maduro on Friday urged an investigation into the killing of his son in anti-government unrest convulsing the OPEC nation for nearly three months.

David Vallenilla, 22, was shot at close range by a military police sergeant on Thursday, apparently with rubber bullets, as youths tried to pull down the fence around an air force base in Caracas and threw rocks at officials who had fired tear gas from inside.

Maduro’s critics said the killing was further evidence of abuse by security forces after protests since April by demonstrators demanding general elections to end 18 years of socialist rule in the South American country amid a deepening economic and political crisis.

At least 75 people have been killed in the protests so far, according to an official count on Friday. The victims include Vallenilla and another youth killed on Monday near the same base. In both incidents, soldiers were caught on camera with guns pointing at the protesters.

“I want to speak to my former colleague of the Caracas Metro, Nicolas Maduro, you know that we worked together, I’m Supervisor Vallenilla ... I was your boss,” said the slain protester’s father, also named David Vallenilla, referring to the years when Maduro worked as a bus driver.

“I want to make sure this is resolved Nicolas, please, he wasn’t a criminal, he was a graduating student ... please friend,” the elder Vallenilla told reporters outside a morgue as tears streamed down his face. “You met him when he was little.”

Reuters was unable to immediately confirm the link between Vallenilla and Maduro.

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Maduro, who makes frequent reference to his former job as a bus driver to highlight his working-class roots, calls the protests an effort to violently remove him from office with the backing of ideological adversaries in Washington.

However, the president condemned the latest “painful” deaths and ordered a newly promoted general to make sure that “nobody else falls.”

Speaking at a Friday event where he gave new positions to several military officials, Maduro said, “The use of firearms is prohibited and I ratify the prohibition.”

Defense Minister Nestor Reverol had earlier offered an unusually swift condemnation of Vallenilla’s shooting by a military officer, and state ombudsman Tarek Saab called it a “vile murder.”

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Opposition leaders have vowed to remain in the streets to demonstrate against what many are now calling a dictatorship and to demand a solution to economic crisis that has created chronic shortages of staple goods and left millions struggling to eat.

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The crisis has brought strong words from world leaders and diplomatic efforts to build dialogue between Maduro and his critics.

At Maduro’s insistence, Venezuela is due to elect a new popular assembly next month to rewrite the constitution. Critics say Maduro will use it to consolidate power and keep adversaries in jail.

Around Caracas on Friday, demonstrators burned tires and blocked roads while chanting slogans that included “No To Dictatorship” and “Murderer, Maduro” to protest Vallenilla’s death.

“We don’t have weapons, the only option we have is to shut down the country,” said Joselyn Almeida who walked out of her office with colleagues to join around 100 people in blocking a main avenue in the upscale district of Las Mercedes.

Officials say the recent wave of street protests across Venezuela, often resulting in vandalism, have arbitrarily restricted free transit and commerce and even prevented ambulances from reaching hospitals.

A group of demonstrators on Friday returned to the spot where Vallenilla was killed. They set three trucks on fire and pushed one of them against the fence of the air base, which they later partially tore down.

Opposition leaders said the demonstrators were not part of the broader protest and insisted the incident was staged by the government to tarnish the protest movement.