Barclays Plc and Citigroup approached South African competition regulator with information relating to the alleged rigging of the rand currency's exchange rate, two sources with direct knowledge of the matter said on Friday.
South Africa's Competition Commission said on Wednesday it had found more than a dozen local and foreign banks colluded to coordinate trading in the South African and U.S. currencies.
Its inquiry centered on an instant messaging chat room called "ZAR Domination", which the Commission alleged was used by the banks to coordinate trading activities when giving quotes to customers who buy or sell currencies.
The Commission launched the probe in April 2015, joining a global clampdown that has led to dozens of traders being fired and big banks fined a total of around $10 billion for rigging interest rate and foreign exchange benchmarks.
In the case of the alleged rigging of the rand, the Competition Commission said it had recommended fines amounting to 10 % of the banks' South African annual revenues to the country's Competition Tribunal, which adjudicates on the watchdog's findings.
"Barclays and Citigroup offered to co-operate with the investigation," one source said, adding that if the information they provided led to a successful prosecution of other members of the alleged cartel they could be exempted from any fine.
Barclays reiterated on Friday a statement made earlier in the week in which it said it was cooperating with regulators, while Citigroup, which has also said it is working with regulators, was not immediately available for comment.
Barclays and Citigroup were not included in the list of banks that the Commission recommended should be fined, but it did name them as members of the alleged rigging group.
The Commission was not seeking any penalty against Citigroup, Barclays or Barclays Africa because of the information they supplied was enough to refer the matter to Tribunal for prosecution, another source said.
The information the banks provided, which the sources did not detail, would be examined by the Competition Tribunal.
The other banks and brokerages named in the case were, Nomura, Standard Bank, Investec, JP Morgan, BNP Paribas, Credit Suisse Group, Commerzbank AG, Standard New York Securities Inc, Macquarie Bank, Bank of America Merrill Lynch (BAML), ANZ Banking Group Ltd and Standard Chartered Plc.
Anglo-South African investment bank and asset manager Investec said on Friday the case against it related to the conduct of just one trader.
"The bank intends to seek further information from the Competition Commission with respect to the specifics of the charges in order to continue to co-operate with them in this regard," it said in a statement.
Officials at Standard Bank, BAML, Commerzbank, BNP Paribas Nomura, Credit Suisse, ANZ, Standard Chartered and Macquarie declined to comment. The others have not commented.