About 100 government supporters have burst into Venezuela’s opposition-controlled National Assembly, where they beat up several lawmakers.
Witnesses said the confrontation came after an assembly session to mark the country’s Independence Day.
Military police guarding the site stood by as intruders brandishing sticks and pipes broke through the gate, AFP news agency said.
The government has vowed to investigate.
“I will not be complicit in acts of violence,” said President Nicolás Maduro.
About 350 people were besieged for hours, including journalists, students and visitors, according to the assembly’s speaker Julio Borges.
Mr Borges also named five of the lawmakers injured. Some were taken away for medical treatment, including Deputy Américo De Grazia, who was carried out on a stretcher.
Venezuela has been shaken by often violent protests in recent months and is in economic crisis.
“This does not hurt as much as seeing every day how we are losing our country,” deputy Armando Armas told reporters as he got into an ambulance, his head swathed in bloody bandages.
The US state department condemned the violence, calling it “an assault on the democratic principles cherished by the men and women who struggled for Venezuela’s independence 206 years ago today”.
AFP, whose journalists were at the scene, said reporters were ordered to leave by the attackers, one of whom had a gun.
Before the intruders rushed the building, Vice-President Tareck El Aissami made an impromptu appearance in the congress with the head of the armed forces, Vladimir Padrino López, and ministers.
Mr El Aissami gave a speech urging the president’s supporters to come to the legislature to show support for him.
A crowd had been rallying outside the building for several hours before breaking into the grounds.
A statement from the the ministry of communication said, the government had ordered an investigation “to establish the whole truth, and on that basis, to apply sanctions to those responsible”.
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