CARACAS (Reuters) - Venezuelan authorities over the weekend admonished the opposition-run National Assembly for reinstating three lawmakers banned over fraud accusations, heightening the power conflict in the crisis-hit OPEC nation.

In Thursday's session, the National Assembly voted to welcome back three opposition legislators from the southern jungle state of Amazonas. The government-leaning Supreme Court had suspended them in January pending a probe of allegations of vote-buying.

Rejecting criticism that it is dragging its feet on the case, the Supreme Court said on Sunday it was currently collecting evidence and stressed its decisions should be respected.

It is unclear when it may issue a ruling in the case.

Also over the weekend, the office of the Attorney General called on the National Assembly to remove the three lawmakers, warning the body was otherwise in contempt of court.

"With these baseless actions, the National Assembly is currently illegal and illegitimately constituted," it said in a statement, stressing Congress' decisions would also be invalid.

With Venezuela mired in economic crisis, the opposition has become more militant recently, trying to replace Supreme Court judges it deems biased and protesting in the streets to demand a recall referendum against President Nicolas Maduro.

Incorporating the three Amazonas lawmakers would hand the opposition a total of 112 legislators, meaning it would command a two-thirds super majority in the 167-seat National Assembly, technically giving it wider powers.

But the Supreme Court has curtailed the Assembly's power time and time again ever since the opposition majority took over in January.

This latest institutional tussle adds to tensions in the South American oil producer of 30 million people, which is enduring a third year of recession, the world's highest inflation and huge lines at shops to obtain scarce food and medicines.

The Democratic Unity opposition coalition says 17 years of socialism have destroyed the economy. It wants to oust Maduro, who won an election to replace Hugo Chavez in 2013, via a referendum.

"To emerge from this crisis we need to emerge from this government, because the government is the crisis," tweeted National Assembly President Henry Ramos on Sunday.

Maduro says foes, backed by Washington, are seeking a coup and carrying out an "economic war" against his government.

Socialist Party heavyweight and former National Assembly president Diosdado Cabello had warned that reinstating the banned legislators could land them in jail.

(Reporting by Daniel Kai and Alexandra Ulmer; Editing by Sandra Maler)