A South Africa court on Wednesday set aside the findings of an investigation that cleared all government officials of corruption over a multi-billion dollar arms deal in which ex-president Jacob Zuma was a suspect.

The four-year inquiry into the scandal released a report in 2016 concluding that there was no evidence to support widespread allegations of bribery, fraud and corruption.

But a High Court in Pretoria on Wednesday found that the inquiry "committed significant errors of law".

The court decided to annul the findings of the inquiry, which was led by Judge Willie Seriti, because of "a set of errors of law, a clear failure to test evidence of key witnesses, a refusal to take account of documentary evidence which contained the most serious allegations which were relevant to its inquiry".

It said investigators approached critical witnesses with "a complete failure to rigorously test the witness by putting questions to them with the required open and enquiring mind."

The arms deal worth around $2 billion saw the government acquire a vast range of military equipment, including fighter jets, helicopters, warships and submarines from countries including Britain, France and Sweden.

Critics have long charged that the government-appointed inquiry was toothless and was being used in an attempt to put the issue to rest.

Zuma, who was forced to resign by the ruling ANC party over corruption scandals, has also been charged with 16 counts of graft linked to a 1990s arms deal made before he became president.

He is accused of taking bribes from French defence company Thales during his time as a provincial economy minister and later as deputy president of the African National Congress (ANC).

He is due back in court on October 15 in connection with the case.