Venezuela's opposition said it will not participate in "fraudulent and illegitimate" presidential elections scheduled to take place on April 22.

The announcement came as President Nicolas Maduro called snap legislative elections in Venezuela on Wednesday to coincide with the vote.

In a statement, the opposition Democratic Unity movement said the "premature" elections were "lacking proper conditions".

"[It] is just a show by the government to give an impression of legitimacy that it does not have," it said.

"In the name of the immense majority of Venezuelans, we challenge the Maduro government to measure itself against the people in real elections."

Democratic Unity issued several demands if it were to participate, including holding the vote in the second half of 2018 and inviting independent international observers.

The move means there is currently only one confirmed candidate to challenge Maduro, 55. Little-known evangelical pastor Javier Bertucci announced his candidacy on Sunday.

Venezuela's Constituent Assembly voted to bring presidential elections forward in late January.

Meanwhile, Maduro called on Wednesday for snap legislative elections in Venezuela, proposing to bring them forward by nearly two years to coincide with the presidential poll.

He also hit back at the opposition coalition for saying it wouldn't participate. "We are going to the elections come rain, shine or lightning, with or without the MUD," said Maduro.

The opposition's most popular leaders are almost all sidelined from politics - jailed, in exile, or barred from holding office.

A coalition of more than a dozen Latin American countries rejected Venezuela's call for early elections, saying it contradicts democratic principles.