Singaporean police said on Monday they had arrested 18 people believed to be part of a multi-million-dollar illegal soccer betting ring less than a month before the World Cup starts.

The suspects are "believed to have received illegal soccer bets amounting to an estimated S$8 million ($6.4 million) in the past two weeks alone", the force said in a statement released on its website.

It did not reveal the nationalities of the suspects, 16 women and two men, who were detained during raids on Sunday and Monday.

Cash totaling S$1.4 million as well as computers, mobile phones and documents detailing betting and bank transaction records were seized during the raid, police said.

"Bookmakers and bettors who assume that they can hide behind the anonymity of the Internet to commit criminal offences should think twice," deputy assistant commissioner of police Kenny Tan warned in the statement.

"The police will find them and prosecute both bookmakers and bettors alike to the fullest extent of the law."

If convicted, the suspects face fines of between S$20,000 and S$200,000 and up to five years in jail.

Sports betting is deeply entrenched in wealthy Singapore, with top European league matches the most favored among punters.

The Singapore Totalisator Board, which manages the country's two legal soccer betting and lottery companies, saw revenues of $983.3 million in the year to March 2013, from a total population of just 5.4 million.

Experts say there are dozens of illegal soccer betting outfits in the city-state. Last year, Singaporean police nabbed 14 people believed to be members of a global match-fixing syndicate, including the suspected mastermind, Dan Tan.

In June last year, three Lebanese referees were convicted by a Singaporean court of accepting sexual services in return for fixing future games.

Singaporean businessman Eric Ding, who is accused of offering the bribes, is currently on trial.

The recent arrests in Singapore comes just days after the Doha-based watchdog group International Center for Sport Security warned in a report that Asian-dominated criminal groups are laundering more than $140 billion of illegal sports betting, mainly on soccer.

The report, which also involved researchers from Sorbonne University in Paris, said Asia accounts for 53 percent of the global illegal sports betting market.

Apart from soccer and cricket, it said tennis, basketball, badminton and motor racing are also affected by illegal sports betting.

Globally, wagers worth between $275 billion and $685 billion are made each year, with more than 80 percent made illegally.