Venezuelan security forces have surrounded the public prosecutor’s office in Caracas in what the chief prosecutor has called a “siege”.
It came a day after the embattled government inaugurated a new legislative body, the 545-member constituent assembly.
Chief prosecutor Luisa Ortega had asked a local court to halt the inauguration.
She cited allegations that the government had misrepresented the results of the vote that created it.
“I reject the siege of the headquarters of the public prosecutor’s office,” Ms Ortega, a leading critic of President Nicolas Maduro, wrote on Twitter on Saturday.
“I denounce this arbitrary act before the national and international community.”
President Maduro says the constituent assembly – which is due to begin work on Saturday – is needed to bring peace after months of crisis sparked by the country’s economic implosion.
But the opposition says the new body, which has the ability to rewrite the constitution, is a way for the president to cling to power.
On Friday in Caracas, police used tear gas against opposition protesters who tried to reach parliament.
Several people were injured as security forces tried to disperse a few hundred demonstrators, reports say.
In other parts of the city, thousands of government supporters gathered to cheer and wave flags as the new members took office. Some carried pictures of late leader Hugo Chávez and the independence hero Simón Bolivar.
Among those sitting for the first time in the 545-member assembly are Mr Maduro’s wife and son.
A close ally of Mr Maduro, former foreign minister Delcy Rodriguez, was elected president.
Her opening speech attacked the opposition as “fascist” and warned the international community against interfering.