The African National Congress (ANC) is not worried about the "revelations" the Democratic Alliance (DA) claimed to have found in the contents of the so-called "spy tapes", it said on Tuesday.

DA leader Helen Zille's assertions that the tapes provided enough evidence to apply for a review of the withdrawal of charges against President Jacob Zuma was a continuation of the party's battle to discredit the ANC and its leadership, said its spokesperson Zizi Kodwa.

"We are neither surprised nor worried by the newly founded revelations of the DA on the contents of the recordings," he said in a statement.

He said the ANC believed that the then acting national director of public prosecutions Mokotedi Mpshe had been competent and had applied his mind in deciding to drop the charges.

The ANC called the DA's interest in the spy tapes a fishing expedition.

On Monday, DA leader Helen Zille said there was "sufficient evidence" on the recordings for a review application of the decision to withdraw corruption charges against Zuma.

"I have read the transcripts of the tapes handed to us by the NPA [National Prosecuting Authority] last Thursday. They constitute recordings of 36 conversations over five months," Zille said in the DA SA Today newsletter.

"Without revealing the contents, I am satisfied that the 'spy tapes' provide sufficient evidence to continue our review application of the decision, by the then acting National Director of Public Prosecutions Mokotedi Mpshe, to withdraw the charges against President Zuma."

The DA's lawyers had advised it not to make public the contents of the tapes.

The DA was handed the spy tapes last week after the Supreme Court of Appeal ruling that the NPA had to comply with a previous order to release the tapes. Zuma had opposed the move.

The recordings, internal memoranda, reports and minutes of meetings dealing with the contents of the recordings had to be provided.

The tapes, containing recorded phone conversations, allegedly reveal collusion between the former head of the Directorate of Special Operations (the now defunct Scorpions) Leonard McCarthy, and the NPA's former head Bulelani Ngcuka to manipulate the prosecutorial process before the ANC's Polokwane conference in 2007.

Zuma was elected ANC president at the conference. Former president Thabo Mbeki had been a contender for another term.

At the time, Mpshe said the tapes showed there was a political conspiracy against Zuma and so the case against him could not continue. The charges were dropped shortly before Zuma was sworn in as president in 2009.

DA national spokesperson Marius Redelinghuys said on Tuesday that if the ANC was really keen to put the matter to bed, as it claimed, South Africans would have heard first-hand the content of the tapes.

"There was something fishy about the president's prolonged and desperate attempts at making the spy tapes disappear along with the 783 charges against him from the start of this saga five years ago," he said.

"It is increasingly difficult for the ANC to keep their 'big fish' off the hook as all indications point to the fact that President Jacob Zuma is an increasing liability for the governing party."