Opposition parties in South Africa have gone to the courts to contest the dismissal of corruption charges against the head of the ruling party, Jacob Zuma. The development comes amid rising controversy over the dismissal which Zuma says proves his innocence.

South African opposition parties are asking a high court to review the decision to drop corruption charges against African National Congress President, Jacob Zuma and are pushing for criminal charges against Zuma's lawyers.

The National Prosecuting Authority, NPA, this week ended a lengthy investigation saying recorded telephone conversations between a senior NPA investigator and the former head of the group showed that there had been political interference in the Zuma case.

The head of the Independent Democrats party, Patricia de Lille, said on national radio that this allegation should be investigated separately but the charges against Zuma should not be dropped. 

"The issue of interference in the independence of the NPA is a completely separate matter from the substantive evidence against Jacob Zuma. It's a criminal offense for anybody to interfere with the independence of the NPA," she said.

Opposition leaders accused Zuma's lawyers of being illegally in possession of classified government information. The recordings were reportedly made by the National Intelligence Agency which said it was launching an investigation into the matter.

The spokesman for the Congress of the People, Phillip Dexter, said no evidence of a political conspiracy had been presented. 

"What there possibly is, is evidence of another conspiracy. And that's the conspiracy to stop the charges being brought against Jacob Zuma. Those tapes should not have been given to any private individual. They are the property of the state and we would like to know how those tapes got into the hands of Mr. Zuma's attorneys," he said.

Zuma had been charged with accepting gifts to thwart a multi-billion dollar arms deal in which millions of dollars worth of bribes had been paid. Zuma said the case was meant to ruin his political career and the dismissal of the charges vindicated him. 

"My quarrel with the NPA was on the methods and the motives of the investigation. The probe was supported by a vicious media campaign designed to find me guilty in the court of public opinion," he said.

But the leader of the Democratic Alliance, Helen Zille, said her party had asked for a judicial review of the dismissal because Zuma needed to have his day in court. 

"He [Zuma] has been charged. The charges were before a court of law. But he's never answered those charges in a court of law. Therefore this is not an acquittal and in fact Jacob Zuma now loses the presumption of innocence," she said.

Zuma is widely expected to become South Africa's next president in elections in two weeks.

He said the dismissal of the charges removed the cloud of suspicion over his head. But many analysts say the case is not likely to go away and opposition parties seem determined to prove them right.