Venezuela's pro-government constituent assembly unanimously adopted a decree Friday giving it the authority to pass legislation on a range of issues affecting security and sovereignty.
The step came after the leadership of the opposition-controlled National Assembly refused to swear an oath of loyalty to the pro-government body, which was installed earlier this month.
National Assembly President Julio Borges slammed the constituent assembly's power-grab in a tweet.
"The constituent assembly and all its acts are illegal and unconstitutional," said Borges. "This decision won't be accepted by the National Assembly, the international community or the people."
The opposition boycotted last month's vote to elect the 545-member assembly, and has accused President Nicolas Maduro of seeking to turn the country into a dictatorship.
Read more: What is going on in Venezuela?
The US State Department issued a statement condemning the constituent assembly's move, saying it undermines democratic institutions in the country.
"This power grab is designed to supplant the democratically-elected National Assembly with an authoritarian committee operating above the law," said the statement.
Maduro says the assembly, which will be tasked with re-writing the constitution, is necessary to facilitate a return to security and stability in the country. Venezuela has been rocked by months of anti-government protests, resulting in more than 120 deaths and dozens of arrests.
Prosecutor flees to Colombia
Venezuela's former top prosecutor Luisa Ortega arrived in Colombia on Friday. She said she feared for her life after the constituent assembly was given power in Venezuela. The body fired her during its first session and there have also been calls for her to be prosecuted, though no charges have been officially filed.
"This afternoon the attorney general of Venezuela Luisa Ortega Diaz arrived from Aruba in a private plane to Bogota's airport and completed the corresponding migration process," Colombia's migration agency said in a statement.
Read more: Oil-rich but cash-starved Venezuela could be close to bankruptcy
Ortega and a number of countries around the world have refused to recognize the assembly and urged the Venezuelan government to restore democracy. Earlier this week, Caracas summoned Germany's ambassador to Venezuela after Berlin called for an end to "arbitrary arrests and excessive violence against the opposition."
ls,nm/sms (AFP, AP, dpa)