Venezuela's President Nicolas Maduro has put the military on alert, stepping up security after a rogue police detective claimed responsibility for a grenade and gunfire attack on state institutions. 

Authorities in the capital, Caracas, said several grenades were hurled at the Supreme Tribunal from a helicopter and 15 bullets were fired at the interior ministry at sunset on Tuesday.

The attack was claimed in a video released online by a man identified by media and the government as 36-year-old Oscar Perez.

On Wednesday, Venezuela Vice President Tareck El Aissami said the helicopter was found near the coast in Vargas state.

During an interview with state television VTV, El Aissami said, "Despite the adverse climate conditions our Bolivarian National Army have found the helicopter used yesterday in two terrorist attacks against institutions."

"Until now, nobody has been arrested," he said. "We are deploying special forces in all the area, and we ask the support of the people."

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Maduro, who has faced months of violent anti-government protests, said the "terrorist attack" was part of an "escalation" by right-wing "coup" plotters against the ruling Socialists. Yet, opponents suspected the raid might had been a hoax to justify repression amid a worsening economic and political crisis.

"I have activated the entire armed forces to defend the peace," Maduro said on Wednesday in remarks broadcast from the Miraflores presidential palace.

No one was injured in the incident.

Beyond his police work, the alleged pilot of the helicopter, Perez, acted in a Venezuelan action film called "Suspended Death", and has posted photographs on social media of himself posing with weapons.

"We are a coalition of military, police and civilian public servants ... opposed to this transitional, criminal government," Perez said in the video, flanked by four masked figures in black, two of them holding rifles.

Al Jazeera's Teresa Bo, reporting from Caracas, said the opposition members were worried about whether the government was going to use the attack as an excuse for further crackdown on dissent.

"We have heard the government and the president accusing students protesters and those who attacked military bases last weekend of terrorism. So nobody really knows what the government's response is going to be to this latest incident," she said.

Julio Borges, opposition legislative speaker, said: "Some people say it is a hoax, some say it is real, some say that it was police personnel who really are fed up."

"Whatever it is, it is very serious. It all points to one conclusion: that the situation in Venezuela is unsustainable," he said.

Another senior opposition legislator, Freddy Guevara, urged people to take part in anti-government rallies on Wednesday - the latest in nearly three months of daily streets protests that have left 76 people dead.

Maduro has for months been fending off calls for elections to replace him from opponents who blame him for the country's worsening crisis.

But the president has so far retained the public backing of the military high command - a factor that analysts say is decisive if he is to remain in power.

Venezuela has seen three attempted military coups since 1992.

Source: Al Jazeera and news agencies