A South African court has revised a 2009 decision to drop graft charges against President Jacob Zuma, saying he should again face a trial over a controversial arms deal in 1999.

“The decision... to discontinue the charges against Mr Zuma is irrational and should be reviewed and set aside,” Judge Aubrey Ledwaba ruled on Friday, adding, “Mr Zuma should face the charges as applied.”

The verdict allows prosecutors to re-open charges against Zuma in connection with a multi-billion dollar arms deal 17 years ago. The embattled leader has denied allegations of accepting bribes from international arms manufacturers at the time.

A court dropped the charges against Zuma shortly before he was to contest presidential votes in 2009, saying tapped phone calls between senior officials in then-president Thabo Mbeki's administration showed that the case was politically motivated.

However, the main opposition party, the Democratic Alliance, fought a long legal battle to revive the 783 charges of corruption, racketeering, fraud and money laundering dating linked to the arms deal scandal.

“Today is a great victory for the rule of law. Ultimately Jacob Zuma must face prosecution," DA leader Mmusi Maimane said after attending the court hearing, adding, “We are deeply, deeply delighted. Jacob Zuma must have... his day in court.”

Sources said Zuma would launch an appeal, further complicating the legal and political wrangling.

“These charges were formally withdrawn... and as such there is no pending litigation before court against President Zuma,” the presidency said in a statement, adding, “The President has noted the decision of the court and will give consideration to the judgment and its consequences.”

Zuma lost another case last month over his illegal use of state funds for renovating a private residence.