Venezuelan troops on Thursday fired what appeared to be rubber bullets at protesters attacking the perimeter of an airbase and a demonstrator was killed, bringing renewed scrutiny of the force used to control riots that have killed at least 76 people.

At least two soldiers shot long firearms through the fence at protesters from a distance of just a few feet. One man collapsed to the ground and was carried off by other protesters, television footage showed. Paramedics took at least two other injured people to a hospital, a Reuters witness said.

The protesters who attacked the fence outside La Carlota airbase in the wealthy east of Caracas, earlier burned a truck and a motorbike when security forces firing rubber bullets broke up a march destined for the attorney general’s office.

David Jose Vallenilla, 22, died after arriving at a hospital in the Chacao municipality where the protest happened, the mayor said. “He died at a private clinic where he arrived in very bad condition,” said Mayor Ramon Muchacho.

Hundreds of thousands of Venezuelans have taken to the streets over the past months to protest a clampdown on the opposition, shortages of food and medicine and President Nicolas Maduro’s plan to overhaul the constitution.

The reaction of the security forces to provocation from protesters has been in the spotlight since images showed a national guard pointing a pistol at protesters on Monday.

Opposition lawmaker Jose Manuel Olivares said Vallenilla had been killed by the national guard firing rubber bullets at point blank range. Olivares, whose arm was wounded in the protest, called for sit-ins on highways on Friday and protests at military bases on Saturday.

Vallenilla suffered wounds to the lungs and heart, a doctor who attended him told Reuters. Reuters could not independently confirm that Vallenilla was the shooting victim shown in television footage. The attorney general’s office said he was shot three times.

“The troops found responsible for crimes will be presented before the law,” said Interior Minister Nestor Reverol, calling on the opposition to stop violent protests.

Maduro says the violence is part of a foreign-led plot to overthrow his government and criticizes the opposition for fanning it, however authorities have taken action against three national guard sergeants accused of killing a boy on Monday.

A small group of protesters throwing petrol bombs and powerful fireworks from behind flimsy homemade shields was able to rip down a section of the fence surrounding the airbase, despite volleys of tear gas and rubber bullets.

At least one soldier aimed a shotgun through the fence, Reuters pictures showed. The national guard uses shotgun cartridges filled with small rubber balls in protests.

Venezuela’s national guard is a wing of the military charged with internal public order. It mainly uses tear gas, water cannons and rubber bullets to control protests that frequently escalate into riots.

On Monday, a teenager died during another protest in the same area after footage showed a national guard soldier pointing a pistol at protesters. After that incident, Maduro moved the head of the national guard to a new position looking after security in the capital, part of a reshuffle that brought several more military figures into his cabinet.

“I have ordered an investigation to see if there was a conspiracy behind this,” Maduro said earlier on Thursday, saying the men involved in Monday’s shooting had been detained.

The office of the attorney general, a former Maduro loyalist who has turned against him over his push to rewrite the constitution, named three national guard sergeants on Thursday, saying they were charged with homicide for that shooting and that a court had put them in custody.