By Daniel Kai and Diego Oré

CARACAS (Reuters) - Venezuela's opposition-run National Assembly defied President Nicolas Maduro's government and ratcheted up a conflict of powers on Thursday by reinstating three lawmakers banned over fraud accusations in the December parliamentary vote.

With the OPEC member mired in economic crisis, Venezuela's opposition has become more militant in recent days, trying to replace Supreme Court judges it deems biased and protesting in the streets to demand a recall referendum against Maduro.

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

"A flawed ruling like this one ...cannot take away the power given us by the people of Amazonas, to be their voice, their legitimate representatives in parliament," said Romel Guzamana, wearing a feathered cap for his indigenous roots.

Government legislators shouted "illegal," while opposition members yelled "112" - in reference to the opposition's 112-seat majority if the three Amazonas parliamentarians are counted.

The number is important, because with 112 members, the opposition would command a two-thirds super majority in the 167-seat National Assembly, giving it potentially wider powers.

Thursday's move adds to extreme 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 election to replace Hugo Chavez in 2013, via a referendum.

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

Thanks to voter anger over the economy, the opposition won the National Assembly in December. But the Supreme Court, which for years has ruled in favor of the ruling socialists, has shot down all the parliament's major initiatives.

"If we say baby Jesus comes in December, the Supreme Court rules it unconstitutional!" satirized opposition legislator Freddy Guevara during a rowdy debate on the Amazonas politicians.

Former parliament president Diosdado Cabello had warned that reinstating the banned legislators could land them in jail.

Hector Rodriguez, who heads the government's parliamentary bloc, said there was proof the three participated in election crimes. "This is totally illegal, unconstitutional," he said during Thursday's session.

A fourth government member elected for Amazonas, also suspended pending the investigation, did not show up.

(Writing by Andrew Cawthorne; Editing by Dan Grebler)