Venezuela's Supreme Court has declared that the new opposition-dominated National Assembly's decisions are void until it unseats three barred parliamentarians.

Monday's ruling brings the South American country caught in an economic crisis worsened by falling oil prices, closer to a showdown over power in the legislature.

Opponents of the socialist revolution launched by Hugo Chavez recently took control of the National Assembly for the first time in 17 years.

The election of the three MPs has been questioned by the ruling socialist party, and the high court had previously barred them from taking their seats - to give officials time to look into allegations of electoral fraud.

That ruling angered members of the opposition, who called it an attempt to undermine their historic victory in legislative elections in December, and they swore the parliamentarians in anyway.

They accuse the Supreme Court of being an arm of President Nicolas Maduro's socialist government and of seeking to steal away its two-thirds majority in the National Assembly with the ruling.

Some in the opposition denounced the ruling as a coup and vowed to continue defying the court.

"We will not cede one iota of the power that the people of Venezuela gave us," Freddy Guevara, an opposition politician, said.

Al Jazeera's Virginia Lopez, reporting from Caracas, said: "One of the possible consequences is that Maduro will now be addressing the country in his yearly State of the Union speech, not from the National Assembly but rather from the Supreme Court."

The opposition plans to introduce an amnesty law on Tuesday for jailed politicians and activists, while government politicians intend to push for a declaration of "national emergency" over the economic crisis.

The opposition also wants to sack Supreme Court justices sworn in by the then socialist-led congress last month, which the opposition said would then allow for the ban on the three lawmakers to be lifted.