Venezuelan opposition figure Juan Guaidó was denied entry to the National Assembly to be re-elected as its head.
Dissident opposition politician Luis Parra, Mr Guaidó’s rival, then declared himself parliament’s new Speaker by megaphone – a move denounced by the opposition as a “parliamentary coup”.
The opposition also said Mr Parra was sworn in without votes or quorum.
In a heated exchange at the doors, Mr Guaidó reportedly told a security officer: “This is unprecedented!”
Images later showed him and other politicians who support him trying to climb a fence to gain entry to the building in the capital, Caracas.
Ahead of the vote, Mr Guaidó had accused the government of attempting to thwart his re-election as parliamentary speaker by bribing and intimidating politicians.