Four grenades were hurled at the high court from a helicopter and bullets were fired at the interior ministry on Tuesday, Maduro said, in a potentially dramatic escalation of the violence gripping the oil-rich South American country.
The attack was claimed in a video released online by a man identified by media and the government as 36-year-old Oscar Perez.
Beyond his police work, Perez has acted in a Venezuelan action film, "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," said Perez, flanked by four masked figures in black, two of them holding rifles.
Maduro has for months been fending off calls for elections to replace him, from opponents who blame him for a desperate economic crisis that has sparked hunger and deadly violence.
He so far retains 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.
Army on alert
The government named Perez as the author of the attack, saying he had stolen a police helicopter.
No one was hurt in the incidents, Maduro said.
He branded the attack part of an "escalation" by right-wing "coup" plotters.
"I have activated the entire armed forces to defend the peace," he said in remarks broadcast from the Miraflores presidential palace.
"Sooner or later, we are going to capture that helicopter and those that carried out this terrorist attack."
Photos circulating on social media showed a helicopter flying over Caracas as explosions were heard.
In the video published by Venezuelan media, Perez called on Maduro to resign and for early elections to be held.
Hoax or real?
Maduro called on the opposition MUD alliance to denounce the attack, but its leaders said there was not yet enough information to comment.
"Some people say it is a hoax, some say it is real, some say that it was police personnel who really are fed up," opposition legislative speaker Julio Borges told reporters.
"Whatever it is, it is very serious. It all points to one conclusion: that the situation in Venezuela is unsustainable."
Borges said pro-government military officers had scuffled with opposition lawmakers in congress on Tuesday and blocked them in the chamber for several hours.
Another senior opposition lawmaker, Freddy Guevara, urged people to take part in anti-government rallies Wednesday - the latest in nearly three months of daily streets protests that have left 76 people dead.
US plot alleged
The assault on the Supreme Court came a day after Maduro announced the arrests of five opponents he accused of plotting against him to clear the way for a US invasion.
Earlier Tuesday, Maduro warned US President Donald Trump that Venezuela would fight back against such a move.
"If Venezuela were dragged into chaos and violence... we would fight," Maduro bellowed in a speech to supporters.
If a coup prevented his side from fulfilling his contested reform plans, he said, "we would achieve it by arms."
A masked protester stands near a burning barricade in Caracas, Venezuela, Wednesday, June 28, 2017. Source: AP
"I am not exaggerating when I say it would have involved the arrival of American ships and troops in Venezuelan waters, on Venezuelan soil," Maduro said.
The opposition regularly accuses Maduro of repressing and jailing opponents.
The international community has called for mediation to solve the crisis after Vatican-backed talks last year broke down.
