On Monday, the International Criminal Police Organization (INTERPOL) reported that more than 4,000 arrests have been made as part of a global police effort during Euro 2016 which targeted illegal gambling and spanned 11 countries across Asia, according to the Reuters report.

An estimated $13 million-plus was seized during the coordinated raids, which Interpol said was the “most significant in recent years.” Part of Operation SOGA (soccer gambling) VI, the raids were conducted throughout Asia in China, Greece, France, Singapore, Italy, Vietnam, Malaysia, and Thailand on illegal gambling dens estimated to have manipulated $649 million in wagers. It was the sixth investigation by the organization, which facilitates international police cooperation, into football gambling.

Call center-type operations and illegal betting websites were targeted in Aces, a second operation conducted by Interpol in the Philippines, South Korea, Cambodia, Vietnam, and Thailand. Money seized between the two operations totaled more than £10 million; however, it is estimated by Interpol that bets nearing £500 million were handled by the illegal gambling dens during Euro 2016.

Chan Lok-wing, Chief Superintendent and Head of Hong Kong’s Organised Crime and Triad Bureau, said “The number of seizures is the highest and most significant amongst similar operations in recent years. The SOGA operations are important for tackling not just illegal gambling, but also the organised networks behind this and other types of crime,” as reported by the news agency.

The 2016 Euro Football Championships has ignited a massive betting craze across Asia resulting in illegal online gambling seeing a record spike in China as millions of yuan has been wagered on the tournament. All totaled, more than 12,500 arrests were made during the course of the six SOGA operations. Bets totaling almost £4.85 billion were handled by more than 3,400 illegal gambling dens which were closed, and £40m in cash was seized.

While the numbers may look impressive, former senior police officer from Australia, Chris Eaton, who has worked for the Fédération Internationale de Football Association (FIFA), the International Centre for Sports Security in Qatar, and Interpol, told ESPN FC that anti-sport gambling operations, “of the easy-to-detect smaller street operation,” have been coordinated by Interpol in Asia for years, always resulting in a large number of arrests and big dollar seizures. However, Eaton said, billions are being manipulated by the big organized online gambling operators, who escape the attention of these policing efforts, controlling the illegal operations from safe-haven countries like Malaysia and the Philippines. He said, “Only coordinated global government intervention will clean up gambling and save sport, and Interpol would be wiser to encourage this than play with the minor leagues of illegal gambling, according to the news agency report.