A notorious Singaporean match-fixing gang rigged more than 100 football games worldwide in a scam worth millions of dollars, before it was busted this month, a source said Monday.

The source, who has direct knowledge of the case, added there were signs that the syndicate, allegedly led by Singaporean businessman Dan Tan, was involved in violent activity.

However, the source played down suggestions that the gang was responsible for a greater share of the 680 suspicious games reported by European investigators earlier this year.

And the source added that there was no evidence that the gang linked to Dan Tan, full name Tan Seet Eng, was involved in a fixing ring uncovered this month in Australia.

The details have emerged two weeks after Singaporean authorities rounded up 14 people in the wealthy Asian city-state's biggest operation yet against international match-fixing.

The five alleged members still in custody include Dan Tan, according to the source.

They are being held under a section of the criminal code usually employed against criminal gangs which allows for up to a year's detention without trial.

Experts say gangs in Singapore have cultivated links with foreign criminals to fix games in different countries, for the purpose of illegal gambling.

Interpol chief Ronald Noble has said the industry has revenues of billions of dollars a year.

After the arrests in Singapore, Noble said the gang was the world's "largest and most aggressive match-fixing syndicate, with tentacles reaching every continent".

Noble, who had previously called for Dan Tan's arrest, added that "the mastermind was someone many believed was untouchable".

European police agency Europol reported in February that hundreds of games worldwide, including World Cup qualifiers and UEFA Champions League ties, had been targeted by fixers.

Tan has been assisting investigators in Singapore since February. He is wanted in Italy and Hungary over match-fixing allegations.

The source said Singaporean investigators had reviewed Europol's evidence and found that much of it was "circumstantial" or included inadmissible items such as wiretaps.

The source could not confirm whether there were other Singapore-based match-fixing rings.

The city-state's links with match-fixing have been in the spotlight since the arrest and jailing of Singapore's Wilson Raj Perumal for match-fixing in Finland.

Perumal, who claims to be a former associate of Tan's, is now reportedly under police protection in Hungary.

However, reports have named him as a suspect in a multi-million-dollar fixing ring revealed this month in Australia's state league.