Singapore police Monday said they have arrested 15 people in a crackdown on illegal betting during intense World Cup fever in the city-state, which has become notorious for football-linked crime.

"Preliminary investigations revealed that the suspects are believed to have received illegal bets amounting to about Sg$800,000 (US$641,000) in the past two weeks," the Singapore Police Force said in a statement posted on its website Monday.

The suspects, 14 men and one women aged between 23 and 70, were detained in raids on Saturday, police said.

It did not reveal their nationalities and a police spokeswoman declined to specifically link them to betting on matches during the FIFA World Cup, which kicked off on June 12 in Brazil.

Cash totalling Sg$350,000, as well as computers, mobile phones and documents detailing betting and bank transaction records were seized during the raid, police said.

The crackdown is the second against illegal football betting the police have publicly announced in the past month.

On May 19, the police said 18 people were arrested for being part of an illegal football betting ring that received over Sg$8.0 million in bets.

Under Singapore's Betting Act, suspects found guilty of illegal bookmaking can face fines of between Sg$20,000 and Sg$200,000 and up to five years in jail.

Individuals convicted of making bets with illegal betting outfits face fines of up to Sg$5,000, six months in jail or both.

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

The Singapore Totalisator Board, which manages the country's only legalised sports betting and lottery operations, 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 football betting outfits in the city-state, which offer much higher returns compared to legal betting.

In a tell-all book released in April, Singaporean arch match-fixer Wilson Raj Perumal said illegal betting outfits offer a plethora of options to punters not offered by legal betting outlets.

These include 'real-time' betting with limits of up to a few hundred thousand dollars, and quirky bets such as who will win the first throw-in or be the first to receive a yellow card.

In September last year, Singapore police nabbed 14 people believed to be members of a global match-fixing syndicate, including the suspected mastermind Dan Tan, an associate of Perumal.

A Singaporean investigative journalist who has reported extensively on football match-fixing said in a book released this month that Tan's ring had planned to rig the 2014 FIFA World Cup before authorities moved to indefinitely detain them.

The Doha-based watchdog International Centre for Sport Security warned in a May report that Asian-dominated criminal groups are laundering more than $140 billion in illegal sports betting annually.