Former president Jacob Zuma's uMkhonto we Sizwe (MK) party has applied to the country's top court to block the newly elected parliament from sitting this week on the grounds that the May 29 vote was marred by fraud, it said on Tuesday.

The National Assembly is due to convene on Friday for lawmakers to swear the oath of office and elect their speaker, deputy speaker and the country's president.

The challenge from MK comes at a time when South Africa is facing a level of political uncertainty unseen in 30 years of democracy, with no clarity as to who will govern the country when the electoral dust settles.

The African National Congress (ANC), which has been in power since the end of apartheid in 1994, lost its majority but remains the biggest party, and is now negotiating with a range of other parties with diametrically opposed policy aspirations.

MK came a surprisingly strong third, winning 14.6% of the vote which translates into 58 seats in the 400-seat chamber, but despite its success it has alleged vote-rigging took place and threatened to boycott the new parliament.

"The 2024 elections were anything but free and fair," said Sihle Ngubane, MK's secretary-general, in the party's application to the Constitutional Court, which it circulated to media on Tuesday via a WhatsApp group.

The Independent Electoral Commission and other parties said the election was free and fair, and South Africa does not have a history of significant vote fraud.

A new entrant in South African politics, MK gained momentum after Zuma announced in December he would be backing the party and soon became its leader.

The party advocates rewriting the constitution, seizing land from white farmers and nationalising all natural resources including mines.

A longtime pillar of the ANC, Zuma fell out with the party after he was forced to quit as president in 2018 over a string of corruption scandals. He was jailed in 2021 for refusing to give evidence at a public inquiry that found there had been widespread public sector corruption during his administration.

Zuma retains a vast and loyal following, especially in his populous home province of KwaZulu-Natal, where MK won 45.9% of the vote to a humiliating 17.6% for the ANC.

MK's name, which means "Spear of the Nation" in Zulu, was also the name of the ANC's armed wing from the apartheid era, but an attempt by the ANC before the election to prevent its rival from using that name and branding was unsuccessful.