CARACAS, Venezuela — Pro-government militias wielding wooden sticks and metal bars stormed congress on Wednesday, attacking opposition lawmakers during a special session coinciding with Venezuela’s independence day.

Four lawmakers were injured and blood was splattered on the neoclassical legislature’s white walls. One of them, Americo de Grazia, had to be removed in a stretcher while suffering from convulsions.

“This doesn’t hurt as much as watching how every day how we lose a little bit more of our country,” Armando Arias said from inside an ambulance as he was being treated for head wounds that spilled blood across his clothes.

The unprecedented attack, in plain view of national guardsmen assigned to protect the legislature, comes amid three months of often-violent confrontations between security forces and protesters who accuse the government of trying to establish a dictatorship by jailing foes, pushing aside the opposition-controlled legislature and rewriting the constitution to avoid fair elections.

Tensions were already high after Vice President Tareck El Aissami made an unannounced morning visit to the National Assembly, accompanied by top government and military officials, for an event celebrating independence day. The short appearance at the congress by top officials who have repeatedly dismissed the legislators as a band of U.S.-backed conspirators was seen by many as a provocation.

Standing next to a display case holding the founding charter, El Aissami said global powers are once again trying to subjugate Venezuela.

“We still haven’t finished definitively breaking the chains of the empire,” he said, adding that President Nicolas Maduro’s plans to rewrite the constitution — a move the opposition sees as a power-grab — offers Venezuela the best chance to be truly independent.

After he left, dozens of government supporters set up a picket outside the building, heckling lawmakers with menacing chants and eventually invading the legislature themselves. The siege only lifted after seven nerve-wracking hours when police set up a corridor to allow the hundreds of people trapped inside the legislature, including lawmakers and journalists, to leave.

The brazen attack on one of the symbols of Venezuela’s already limping democracy drew widespread international rebuke.

“This violence, perpetrated during the celebration of Venezuela’s independence, is an assault on the democratic principles cherished by the men and women who struggled for Venezuela’s independence 206 years ago today,” U.S. State Department spokeswoman Heather Nauert said.

Despite the violence, lawmakers approved a plan by the opposition to hold a symbolic referendum on July 16 that would give voters the chance to reject Maduro’s plans to draft a new political charter.

Later Maduro condemned the violence, but complained that the opposition doesn’t do enough to control “terrorist attacks” committed against security forces by anti-government protesters.

“I will never be an accomplice to acts of violence,” said Maduro during a speech at a military parade.

The clash followed Tuesday’s appearance of two short videos by a former police inspector who allegedly stole a helicopter and fired on two government buildings last week.

Oscar Perez, repeating a call for rebellion among the security forces, said that he was in Caracas after abandoning the helicopter along the Caribbean coast and was ready for the “second phase” of his campaign to free his homeland from what he called the corrupt rule of Maduro and his “assassin” allies.

Perez gave no other details but pledged to join youth who have been protesting on the streets the past three months against Maduro.

“Stop talking. Get on the streets. Take action. Fight,” he said in the video, sitting before a Venezuelan flag and with what looks like an assault rifle by his side. He also denounced Maduro’s plan to rewrite the constitution.

“If this constitutional assembly goes through, Venezuela will cease to exist because we’ll have given away the country to the Cubans,” he said.

Hours later, another video appeared in which he urged Venezuelans to march on a Caracas military base, not the presidential palace, to locate and remove Maduro along with the ruling elite.

The bold though largely harmless June 27 attack shocked Venezuelans who had grown accustomed to almost-daily clashes since April between often-violent youth protesters and security forces that have left more than 90 people dead and hundreds injured.

Perez apparently piloted the stolen police helicopter that sprayed 15 bullets toward the Interior Ministry and dropped at least two grenades over the supreme court building.

While Maduro claimed Perez had stolen the helicopter on a U.S.-backed mission to oust him from power, many in the opposition questioned whether the incident was a staged by the government to distract attention from the president’s increasingly authoritarian rule.

Adding to the intrigue is Perez’s colorful past.

In 2015, he produced and starred in a film called “Suspended Death,” and several photos show him in fatigues, scuba diving while toting an assault rifle, skydiving and standing in action poses with a German shepherd by his side. In his political debut, he read a manifesto in which he claimed to be part of a group of disgruntled members of Venezuela’s security forces determined to save the country’s democracy.

Perez said in the video that the strike produced no casualties because he had taken care to avoid them. Neither of the buildings he attacked suffered damage. The helicopter he stole was found 24 hours later, abandoned in a verdant valley near the Caribbean coastline outside Caracas.