Groups of armed civilians known as "colectivos" have an infamous reputation in Venezuela where they have been deployed alongside security forces to suppress protests against Maduro.

"Armed colectivos shot at us," wrote lawmaker Delsa Solorzano, a close ally of opposition leader Juan Guaido.

He had been hoping to open a parliamentary session at the National Assembly where armed forces previously prevented him from entering, first for a vote in which we was to be re-elected as the body's president, and then two days later when a rival claimant to the position held his own meeting there.

Guaido has used his position as parliamentary speaker to challenge Maduro's authority and a year ago declared himself acting president.

On Twitter, Guaido said the parliamentary session would be held at an amphitheater in eastern Caracas.

AFP reporters heard what sounded like gunshots around the National Assembly, which had been surrounded by armed forces and militias since early morning.

"They shot at our car," Solorzano tweeted.

Guaido's team shared photos of vehicles with smashed windows while denouncing an "attack."

It also shared videos posted by journalists capturing the moments in which they came under attack from young men in civilian dress, identified as "colectivos" by those media.

"The dictatorship insists ... on using its repressive organs and paramilitary groups," wrote Guaido on Twitter.

- Stolen cameras -

On January 5, armed forces prevented Guaido from entering parliament where a vote on his re-election was due to take place.

In his absence, Luis Parra -- an opposition lawmaker accused of corruption but now backed by Maduro -- proclaimed himself parliament speaker.

Two days later, he held a parliamentary session, attended mostly by regime lawmakers, as armed forces again blocked Guaido.

That day the press workers' union said two reporters had been attacked and robbed of their camera equipment by colectivos.

Venezuela has been in recession for the last five years amidst a crippling economic crisis that has seen poverty soar.

Almost four million people have left the country since the start of 2016.

The opposition accuses Maduro of rigging his 2018 re-election and wants him to resign so it can set up a transitional government and a new vote.

The National Assembly is the only government branch in opposition hands but it has been effectively sidelined since 2017 when Maduro set up a rival parliament made up entirely of regime loyalists.

The supreme court, also filled with Maduro cronies, has since annulled every decision the National Assembly takes.

Parliamentary elections are due later this year in which Maduro has vowed to "take back" the National Assembly.