A South African court on Friday threw out President Jacob Zuma's attempt to appeal against a ruling that he should face almost 800 corruption charges, piling pressure on the embattled leader.

Zuma had tried to overturn a court order that the National Prosecuting Authority (NPA) should reinstate the charges that were dropped in 2009 shortly before he came to power.

The charges relate to alleged corruption, racketeering, fraud and money laundering over a multi-billion dollar arms deal.

The president has battled several corruption scandals while in office, as well as enduring growing criticism focused on South Africa's record unemployment and poor growth rate.

"We seriously considered whether the appeal would have reasonable prospects of success and came to the conclusion that there are no merits in the arguments," Judge Aubrey Ledwaba told the High Court in Pretoria.

"The applications for leave to appeal… are dismissed."

In 2009, state prosecutors justified dropping the 783 charges by saying that tapped phone calls between officials in then-president Thabo Mbeki's administration showed undue interference in the case.

The move cleared the way for Zuma, leader of the African National Congress (ANC) party, to be elected as South Africa's president just weeks later.

The tapped phone recordings, which became known as the "spy tapes", were kept secret until they were released in 2014 after a legal battle fought by the main opposition party, the Democratic Alliance (DA).

The DA hailed the court decision as a victory, and claimed that the charges were automatically reinstated by the ruling.

"The prosecution against President Jacob Zuma must proceed," it said in a statement.

"The NPA must give President Zuma a date by which he is to appear in court."

- Key electoral test -

A government spokesman told AFP that "the presidency noted the court decision and it is being studied".

Pressure for Zuma to resign would increase if some or all of the charges were reinstated.

However he could still petition the Supreme Court of Appeal and even go to the Constitutional Court, the highest in the land.

"The question now will be the role of NPA. Will they protect Zuma?" independent political analyst Daniel Silke told AFP.

"Their position has been murky and the question is will they show allegiance to the country or to the ruling party?"

The ANC faces testing municipal elections on August 3 when the DA and the Economic Freedom Fighters party hope to gain ground with voters frustrated with lack of progress in South Africa since apartheid rule ended in 1994.

"President Zuma's image has suffered a great deal of late, and this decision could not have come at a worse time," Mcebisi Ndletyana, professor of political science at the University of Johannesburg, told AFP.

"The party at this stage cannot do with a president who is facing corruption charges."

Zuma, 74, will have completed two terms in 2019 and is not eligible to run for president again, but the ANC could replace him ahead of the next general election.

In March, the president lost another major legal case when South Africa's highest court found he violated the constitution over the use of public funds to upgrade his private residence.

Source: AFP