* Investigation at advanced stage
* Banks not coming forward with information - watchdog
* Confident evidence can back up case (Adds quotes, details)
By Tiisetso Motsoeneng
PRETORIA, June 8 (Reuters) - South Africa's competition watchdog could hand out some of its biggest fines ever after its investigation into suspected currency-rigging by global banks, it said on Monday.
The Competition Commission has accused dealers at banks of colluding by using an instant messaging chat room called "ZAR Domination", to coordinate their trading activities when giving quotes to customers who buy or sell currencies. ZAR is the South African currency code used in financial markets.
The investigation is part of a global push to probe price-rigging in currency markets.
"We are at an advanced stage and we are quite comfortable and confident what we can back up our case," the head of the Commission, Tembinkosi Bonakele, told Reuters in an interview.
The investigation is focusing on trading in currency pairs involving the South African rand, whose turnover averages between 10 billion and 15 bln rand ($840 million to $1.3 bln) a day.
"It's a big investigation involving massive amounts of turnover and if you just have a look at our guidelines, you can't escape the conclusion that these are going to be fairly significant fines," Bonakele said.
"They would be among the highest fines handed by the Commission."
Under South African law, companies can be fined a maximum of 10 percent of the turnover of a division in which the anticompetitive conduct occurred.
Banks named in the investigation are Barclays Africa , the South African unit of Barclays Plc, Investec, Citigroup, JP Morgan, BNP Paribas, Standard Bank and Standard Chartered .
While Similar foreign exchange price-fixing probes are underway in Europe, Asia and the United States, this is the first time regulators have investigated banks' trading in the South African currency.
Barclays Africa, Standard Chartered and Investec have said they would co-operate with the investigation. The other banks had either previously declined to comment or their officials were not immediately available.
Bonakele said he was disappointed that none of them have launched their own internal investigations or voluntarily come forward with information to fast-track the investigation.
"I don't see the kind of reaction that I would have expected in a very important sector like this," he said. "I take the reactions that say 'we are co-operating' with a pinch of salt."
He declined to say when the case would be filed with the Competition Tribunal, which adjudicates on the Commission's findings. (Editing by James Macharia and Susan Fenton)