South African former president Jacob Zuma said Sunday his new party would join an opposition alliance to coordinate resistance to the government, while maintaining its challenge to the general election results.

The MK said it would join a newly formed parliamentary grouping includes several mostly leftist opposition parties represented in parliament.

Called the "Progressive Caucus" it is currently led by the radical leftist Economic Freedom Fighters (EFF), which won 39 seats in the new parliament.

Despite the "daylight robbery" of votes, parties who form part of this alliance achieved around "30 percent in the national assembly, said uMkhonto weSizwe (MK) party spokesman Nhlamulo Ndhlela said.

That, he said, "puts us in a very strong position to fight on for the total economic liberation of black and African people".

Ndhlela was reading from a statement on behalf of the 82-year-old former president. Zuma, a stern expression on his face, sat quietly as his speech was read out, occasionally answering questions from the press.

"The 2024 elections were rigged" said Ndhlela. "We have instructed our legal team to take any steps possible both inside of South Africa and internationally to ensure that justice is done".

And he added: "At the right time we will call on our people to demonstrate their dissatisfaction against all these injustices peacefully, in the streets, in the court and even in parliament until our grievances are addressed."

The MK came third in the election, winning 14.6 percent of the vote and 58 parliamentary seats.

- An 'unholy alliance' -

On Friday, the party boycotted the country's first parliamentary sitting where Zuma's long-term political foe Cyril Ramaphosa was re-elected as president for a second term.

Although the party said its MPs will now be present in the National Assembly, it also announced it had launched a fresh court bid to dispute the "rigged" election results.

It had already gone to court to try to prevent the new parliament from convening, and lodged a separate complaint over alleged election irregularities.

Several other parties have also complained to the country's electoral body and lodged legal complaints.

Ramaphosa, who will be inaugurated on June 19, will lead what he calls a government of national unity after the May poll produced no outright winner.

The national unity government includes the centre-right Democratic Alliance (DA), the Zulu nationalist Inkatha Freedom Party and other smaller groups.

The deal got a frosty reception from the opposition parties.

Ndhlela for the MK denounced the new coalition as a "white-led unholy alliance" that "must be crushed before it finds its feet". He accused the ANC of going to "bed with the racists".

The EFF dismissed the idea of working with rivals holding radically different political views, such as the DA.

Zuma has been a bitter rival of Ramaphosa's ever since he was ousted by his own party, the African National Congress (ANC), under a cloud of corruption allegations in 2018 and replaced by Rampaphosa.

The new government deal is "meaningless", Zuma said.