Oliphant asked for an investigation several months ago

Another four referees were arrested on Friday morning in Johannesburg and Bloemfontien on match-fixing allegations.

A spokesperson for police commissioner Jackie Selebi said that the latest arrests involved senior referees.

I'm comforted by the fact that the matter will finally come into the open. Now all referees won't be painted with the same brush South African referee Jerome Damon

Police arrested three club officials on Thursday, a week after 10 referees were taken into custody.

"The total number of persons arrested under the Prevention and Combating of Corruption Act under Operation Dribble is now 17. More arrests are expected," spokesperson Sally De Beer said.

In all, 20 referees, players and officials are alleged to have accepted bribes to fix matches.

South African Football Association president Molefi Olifant called for an investigation into claims of bribery and corruption in April.

Bribes were said to have ranged from $1,500 for a Premier Soccer League game to almost $6,500 for cup matches.

Meanwhile one of South Africa's leading referees, Jerome Damon, has backed the on-going investigation.

Damon, who officiated at the African Cup of Nations in Tunisia earlier this year, told BBC Sport that there had for many years been suspicions about referees being bribed by club officials.

"There's always been whispers in the corridors about this issue. At the beginning of the season last August the issue was raised once again," said Damon.

Damon said he hoped the investigation would clear the air surrounding refereeing in South Africa which has come under intense criticism from fans and the media over the past few seasons.

"I'm comforted by the fact that the matter will finally come into the open. Now all referees won't be painted with the same brush.

"Often when things went wrong for a club they would allege that all referees are corrupt.

"Now as the investigation unfolds, specifics are coming to the fore, arrests are being made and names are being mentioned. I'm hoping at the end of it the 'clean' individuals will be vindicated and others will be out of the game," he said.

Damon admitted that referees face a major task to restore the credibility of the game in South Africa.

"It's an immense challenge for all of us in football to ensure the standards are raised.

"We're heading towards 2010 and it's my desire as well as that of my colleagues to be involved in the World Cup in our home country. To do that we need to clean up the perceptions around referees very quickly," he said.